Visor de particules

2026-05-04 09:44:56 +02:00 · 2026-05-04 09:44:56 +02:00 · f6e225de55
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--- a/.gitignore
+++ b/.gitignore
@ -0,0 +1,66 @@
+# --- Entorno y secretos (no subir nunca) ---
+.env
+.env.*
+!.env.example
+!.env*.example
+*.pem
+secrets/
+
+# --- Python (backend) ---
+__pycache__/
+*.py[cod]
+*$py.class
+*.so
+.Python
+venv/
+.venv/
+env/
+ENV/
+*.egg-info/
+.eggs/
+dist/
+build/
+.pytest_cache/
+.mypy_cache/
+.ruff_cache/
+htmlcov/
+.coverage
+.coverage.*
+*.cover
+
+# --- Node / Next (frontend; refuerzo desde la raíz) ---
+node_modules/
+.npm
+.pnp.*
+.yarn/cache
+.yarn/unplugged
+.yarn/build-state.yml
+.yarn/install-state.gz
+
+# --- Salidas de build y caché ---
+.next/
+out/
+.turbo/
+*.tsbuildinfo
+
+# --- Datos / binarios grandes (NetCDF suele ser muy pesado) ---
+*.nc
+
+# --- Logs y temporales ---
+*.log
+npm-debug.log*
+yarn-debug.log*
+yarn-error.log*
+.pnpm-debug.log*
+
+# --- Jupyter ---
+.ipynb_checkpoints/
+
+# --- IDE y SO ---
+.idea/
+.vscode/
+*.swp
+*.swo
+*~
+.DS_Store
+Thumbs.db
--- a/README.md
+++ b/README.md
@ -0,0 +1,107 @@
+# Simulador de Contaminació Marina
+
+Visor web de trajectòries lagrangianes de **~10.000 partícules contaminants** al Mediterrani occidental. Les partícules surten de punts de la costa catalana i es dispersen amb els corrents marins durant 72 hores. Quan arriben a la costa, s’encallen i s’acumulen, mostrant zones d’impacte.
+
+**Stack:** Python · FastAPI · Next.js · Deck.gl · MapLibre (sense claus d’API)
+
+---
+
+## Arquitectura
+
+```
+trajectories/
+├── backend/                 # API i dades
+│   ├── main.py              # FastAPI: metadata, blocs JSON/Arrow, CORS, gzip
+│   ├── data/                # Dades servides per l’API
+│   │   ├── metadata.json    # (opcional) simulació "default" a la arrel
+│   │   └── simulations/     # Una carpeta per simulació
+│   │       └── <sim_id>/   # metadata.json, block_0.arrow, block_1.arrow, ...
+│   ├── etl/                 # Pipeline NetCDF → blocs Arrow + metadata
+│   │   ├── nc_reader.py     # Lectura NetCDF (lon, lat, u, v, beached, temps)
+│   │   ├── pipeline.py      # Orquestració: load_nc → subsample horari → write_blocks_arrow
+│   │   └── to_blocks.py     # Escriptura Arrow IPC + metadata.json
+│   └── scripts/
+│       └── run_etl.py      # CLI: python -m scripts.run_etl fitxer.nc [--sim-id ...]
+│
+└── frontend/                # App Next.js (App Router)
+    ├── src/
+    │   ├── app/page.tsx     # Pàgina principal → TrajectoryMap
+    │   ├── components/      # MapView, MapHeader, TimePlayer, TrajectoryMap, IntroDialog, …
+    │   ├── hooks/           # useBlocks (càrrega Arrow/JSON), useSimulation, useMapLayers, useMetadata
+    │   ├── lib/              # constants, trajectoryData (buildTrails, buildTripsWithTime)
+    │   └── types/            # trajectory (Meta, Block, PointDatum, TripDatum, …)
+```
+
+- **Backend:** Servir `metadata.json` i blocs de frames (JSON o **Arrow IPC**). Les dades viuen a `backend/data/` o `backend/data/simulations/<sim_id>/`. L’API accepta `?sim=default` (o qualsevol `sim_id`) per triar simulació.
+- **Frontend:** Demana metadata a `/api/metadata?sim=...`, després els blocs a `/api/block/{id}` o `/api/block/{id}/arrow`. Construeix trails i trips a memòria (TripsLayer amb timestamps, PathLayer per selecció). Deck.gl + MapLibre renderitzen el mapa; el reproductor temporal avança el `currentTime` i es visualitzen les trajectòries amb color per origen, bloom/glow i partícules actives/beached.
+
+---
+
+## Com arrencar el projecte
+
+### Requisits
+
+- **Backend:** Python 3.10+, Node 18+ (només si no tens les dependències del backend instal·lades)
+- **Frontend:** Node 18+
+
+### 1. Backend
+
+```bash
+cd backend
+
+# Entorn virtual i dependències
+python3 -m venv venv
+source venv/bin/activate   # Windows: venv\Scripts\activate
+pip install -r requirements.txt
+
+# Dades (una de les dues opcions)
+# Opció A: Dades de prova (sense NetCDF)
+python generate_dummy_data.py
+
+# Opció B: ETL des d’un NetCDF (genera block_*.arrow + metadata a data/simulations/<sim_id>/)
+python -m scripts.run_etl path/to/trajectories.nc
+python -m scripts.run_etl path/to/file.nc --sim-id my_run --write-json   # opcional JSON
+
+# Servidor API (port 8000)
+uvicorn main:app --reload
+```
+
+L’API queda disponible a **http://localhost:8000**.
+
+### 2. Frontend
+
+```bash
+cd frontend
+
+npm install
+npm run dev
+```
+
+Obre **http://localhost:3000**. Per defecte el frontend crida l’API a `http://localhost:8000` (configurable amb `NEXT_PUBLIC_API_URL` si cal).
+
+### 3. Ús bàsic
+
+1. Backend en marxa (terminal 1), frontend en marxa (terminal 2).
+2. Obrir http://localhost:3000.
+3. Tancar/acceptar el popup d’introducció i esperar que carreguin els blocs (barra de progrés).
+4. Play / slider / velocitat (×0.5 … ×8). Zoom a les partícules (botó crosshair), Filters (basemap, capes), Info.
+
+---
+
+## API (resum)
+
+| Endpoint | Descripció |
+|----------|------------|
+| `GET /api/simulations` | Llista d’IDs de simulació disponibles |
+| `GET /api/metadata?sim=default` | Metadata (num_particles, num_steps, num_blocks, seed_names, origins, time_start, time_end, …) |
+| `GET /api/block/{id}?sim=default` | Bloc en JSON (frames + step_start, step_end, accumulation) |
+| `GET /api/block/{id}/arrow?sim=default` | Bloc en Apache Arrow IPC (columnes: step, particle_id, lon, lat, u, v, beached) |
+
+---
+
+## Característiques
+
+- **Partícules i temps:** milers de partícules, 72 h (1 pas/hora), blocs de 24 h per càrrega progressiva.
+- **Trajectòries:** TripsLayer amb cap arrodonit, color per origen (paleta), bloom/glow; partícules actives vs beached (vermell).
+- **Mapa:** MapLibre (basemaps Carto), zoom/fit a partícules, tooltip amb origen i velocitat.
+- **Dades:** ETL des de NetCDF (subsample horari, beached persistent) o dades de prova amb `generate_dummy_data.py`.
--- a/backend/pycache/main.cpython-312.pyc
+++ b/backend/pycache/main.cpython-312.pyc
--- a/backend/data/block_0.json
+++ b/backend/data/block_0.json
--- a/backend/data/block_1.json
+++ b/backend/data/block_1.json
--- a/backend/data/block_2.json
+++ b/backend/data/block_2.json
--- a/backend/data/metadata.json
+++ b/backend/data/metadata.json
--- a/backend/data/simulations/sim_08_23/block_0.arrow
+++ b/backend/data/simulations/sim_08_23/block_0.arrow
--- a/backend/data/simulations/sim_08_23/block_1.arrow
+++ b/backend/data/simulations/sim_08_23/block_1.arrow
--- a/backend/data/simulations/sim_08_23/block_2.arrow
+++ b/backend/data/simulations/sim_08_23/block_2.arrow
--- a/backend/data/simulations/sim_08_23/block_3.arrow
+++ b/backend/data/simulations/sim_08_23/block_3.arrow
--- a/backend/data/simulations/sim_08_23/block_4.arrow
+++ b/backend/data/simulations/sim_08_23/block_4.arrow
--- a/backend/data/simulations/sim_08_23/block_5.arrow
+++ b/backend/data/simulations/sim_08_23/block_5.arrow
--- a/backend/data/simulations/sim_08_23/block_6.arrow
+++ b/backend/data/simulations/sim_08_23/block_6.arrow
--- a/backend/data/simulations/sim_08_23/metadata.json
+++ b/backend/data/simulations/sim_08_23/metadata.json
--- a/backend/data/simulations/sim_08_23_test/block_0.arrow
+++ b/backend/data/simulations/sim_08_23_test/block_0.arrow
--- a/backend/data/simulations/sim_08_23_test/block_1.arrow
+++ b/backend/data/simulations/sim_08_23_test/block_1.arrow
--- a/backend/data/simulations/sim_08_23_test/block_2.arrow
+++ b/backend/data/simulations/sim_08_23_test/block_2.arrow
--- a/backend/data/simulations/sim_08_23_test/block_3.arrow
+++ b/backend/data/simulations/sim_08_23_test/block_3.arrow
--- a/backend/data/simulations/sim_08_23_test/block_4.arrow
+++ b/backend/data/simulations/sim_08_23_test/block_4.arrow
--- a/backend/data/simulations/sim_08_23_test/block_5.arrow
+++ b/backend/data/simulations/sim_08_23_test/block_5.arrow
--- a/backend/data/simulations/sim_08_23_test/block_6.arrow
+++ b/backend/data/simulations/sim_08_23_test/block_6.arrow
--- a/backend/data/simulations/sim_08_23_test/metadata.json
+++ b/backend/data/simulations/sim_08_23_test/metadata.json
--- a/backend/etl/init.py
+++ b/backend/etl/init.py
@ -0,0 +1 @@
+# ETL: NetCDF trajectory → Apache Arrow blocks for frontend
--- a/backend/etl/nc_reader.py
+++ b/backend/etl/nc_reader.py
@ -0,0 +1,201 @@
+"""
+Read trajectory NetCDF and return normalized arrays: frames[step][particle] = [lon, lat, u, v, beached].
+Supports common CF / Parcels-style dimensions (time, traj) or (obs, particle).
+Reads actual time axis when present for correct calendar display (e.g. 27/8–3/9 instead of 83 days).
+"""
+
+from __future__ import annotations
+
+import numpy as np
+
+try:
+    import xarray as xr
+except ImportError:
+    xr = None
+
+from .schema import (
+    LON_NAMES,
+    LAT_NAMES,
+    U_NAMES,
+    V_NAMES,
+    BEACHED_NAMES,
+    TIME_NAMES,
+)
+
+
+def _find_var(ds, names: tuple[str, ...]):
+    for n in names:
+        if n in ds:
+            return ds[n]
+    return None
+
+
+def load_nc(
+    path: str,
+) -> tuple[
+    np.ndarray, int, int, list[int], list[str], list[int],
+    str | None, str | None, np.ndarray | None,
+]:
+    """
+    Load a trajectory NetCDF file.
+
+    Returns:
+        frames: shape (num_steps, num_particles, 5) with [lon, lat, u, v, beached]
+        num_particles: int
+        num_steps: int
+        release_steps: list of length num_particles (step index when particle appears)
+        seed_names: list of origin names (may be empty)
+        origins: list of length num_particles (index into seed_names)
+        time_start_iso: ISO datetime string of first time (or None)
+        time_end_iso: ISO datetime string of last time (or None)
+        time_ref_sec: 1D array (num_steps,) of epoch seconds per step for subsampling (or None)
+    """
+    if xr is None:
+        raise ImportError("xarray is required for NetCDF ETL. pip install xarray netCDF4")
+
+    ds = xr.open_dataset(path)
+
+    # Resolve dimensions: time/obs and particle/traj
+    time_dim = None
+    particle_dim = None
+    for d in ds.dims:
+        dlo = d.lower()
+        if dlo in ("time", "obs", "step", "t", "nt"):
+            time_dim = d
+        elif dlo in ("particle", "traj", "n_particles", "trajectory", "pid"):
+            particle_dim = d
+
+    if time_dim is None:
+        time_dim = list(ds.dims)[0]
+    if particle_dim is None:
+        dims = [d for d in ds.dims if d != time_dim]
+        particle_dim = dims[0] if dims else None
+
+    if particle_dim is None:
+        raise ValueError("Could not identify time and particle dimensions in NetCDF")
+
+    lon_var = _find_var(ds, LON_NAMES)
+    lat_var = _find_var(ds, LAT_NAMES)
+    if lon_var is None or lat_var is None:
+        raise ValueError("NetCDF must contain lon/lat (or longitude/latitude) variables")
+
+    lon = np.asarray(lon_var).astype(np.float64)
+    lat = np.asarray(lat_var).astype(np.float64)
+    dims = getattr(lon_var, "dims", None) or ()
+
+    if lon.ndim == 1 and lat.ndim == 1:
+        if len(lon) == len(lat):
+            num_particles = 1
+            num_steps = len(lon)
+            lon = lon.reshape(num_steps, 1)
+            lat = lat.reshape(num_steps, 1)
+        else:
+            raise ValueError("lon/lat 1D but different lengths")
+    elif lon.ndim == 2:
+        if dims == (particle_dim, time_dim):
+            lon = lon.T
+            lat = lat.T
+        num_steps, num_particles = lon.shape
+    else:
+        raise ValueError("lon/lat must be 1D or 2D")
+
+    u_var = _find_var(ds, U_NAMES)
+    v_var = _find_var(ds, V_NAMES)
+    if u_var is not None and v_var is not None:
+        u = np.asarray(u_var).astype(np.float32)
+        v = np.asarray(v_var).astype(np.float32)
+        if u.ndim == 2 and getattr(u_var, "dims", ()) == (particle_dim, time_dim):
+            u, v = u.T, v.T
+        if u.shape != (num_steps, num_particles):
+            u = np.broadcast_to(u.ravel()[: num_steps * num_particles].reshape(num_steps, num_particles), (num_steps, num_particles))
+        if v.shape != (num_steps, num_particles):
+            v = np.broadcast_to(v.ravel()[: num_steps * num_particles].reshape(num_steps, num_particles), (num_steps, num_particles))
+    else:
+        # Derive u, v from lon, lat differences (m/s scale: deg/hour -> rough m/s)
+        deg_per_m = 1.0 / 111_320
+        u = np.zeros((num_steps, num_particles), dtype=np.float32)
+        v = np.zeros((num_steps, num_particles), dtype=np.float32)
+        u[1:] = (lon[1:] - lon[:-1]) * deg_per_m * 111320 / 3600
+        v[1:] = (lat[1:] - lat[:-1]) * deg_per_m * 111320 / 3600
+
+    beached_var = _find_var(ds, BEACHED_NAMES)
+    if beached_var is not None:
+        raw = np.asarray(beached_var)
+        if raw.ndim == 2 and getattr(beached_var, "dims", ()) == (particle_dim, time_dim):
+            raw = raw.T
+        if raw.shape != (num_steps, num_particles):
+            beached = np.zeros((num_steps, num_particles), dtype=np.int8)
+        else:
+            # Normalize: 1 = beached, 0 = not. Ignore fill values (e.g. -2e9, NaN)
+            beached = np.where(
+                (np.isfinite(raw)) & (raw > 0.5),
+                1,
+                0,
+            ).astype(np.int8)
+    else:
+        beached = np.zeros((num_steps, num_particles), dtype=np.int8)
+
+    frames = np.stack([lon.astype(np.float32), lat.astype(np.float32), u, v, beached], axis=-1)
+
+    # Release step: first non-NaN or first step
+    release_steps = []
+    for p in range(num_particles):
+        valid = np.where(np.isfinite(frames[:, p, 0]))[0]
+        release_steps.append(int(valid[0]) if len(valid) else 0)
+    seed_names = []
+    origins = [0] * num_particles
+
+    # Optional: origin/seed from NetCDF
+    if "origin" in ds:
+        o = np.asarray(ds["origin"]).ravel()
+        if len(o) >= num_particles:
+            origins = o[:num_particles].astype(int).tolist()
+    if "seed_names" in ds.attrs:
+        seed_names = list(ds.attrs["seed_names"])
+    elif "seed_name" in ds:
+        sn = np.asarray(ds["seed_name"])
+        if sn.ndim >= 1:
+            try:
+                seed_names = [str(x) for x in sn.values.ravel()[:num_particles]]
+            except Exception:
+                seed_names = [f"Seed {i}" for i in range(max(origins) + 1)]
+
+    # Optional: actual time axis for calendar display and hourly subsampling
+    time_start_iso: str | None = None
+    time_end_iso: str | None = None
+    time_ref_sec: np.ndarray | None = None
+    time_var = _find_var(ds, ("time",) + TIME_NAMES)
+    if time_var is not None:
+        try:
+            t = np.asarray(time_var)
+            if time_var.dims == (particle_dim, time_dim):
+                t = t.T  # (num_steps, num_particles)
+            if t.shape == (num_steps, num_particles):
+                t_flat = t.ravel()
+                valid = t_flat[~np.isnat(t_flat)]
+                if len(valid) > 0:
+                    time_start_iso = str(np.nanmin(valid))
+                    time_end_iso = str(np.nanmax(valid))
+                # Reference time per step (min over particles) in epoch seconds for subsampling
+                time_ref_sec = np.full(num_steps, np.nan, dtype=np.float64)
+                for s in range(num_steps):
+                    row = t[s, :]
+                    row = row[~np.isnat(row)]
+                    if len(row) > 0:
+                        secs = row.astype("datetime64[s]").astype(np.float64)
+                        time_ref_sec[s] = float(np.min(secs))
+        except Exception:
+            pass
+
+    ds.close()
+    return (
+        frames,
+        num_particles,
+        num_steps,
+        release_steps,
+        seed_names,
+        origins,
+        time_start_iso,
+        time_end_iso,
+        time_ref_sec,
+    )
--- a/backend/etl/pipeline.py
+++ b/backend/etl/pipeline.py
@ -0,0 +1,133 @@
+"""
+Orchestrate ETL: NetCDF path → normalized frames → Arrow blocks + metadata.
+Subsamples to one frame per hour when time axis is available (e.g. 5-min → hourly).
+"""
+
+from __future__ import annotations
+
+from pathlib import Path
+
+import numpy as np
+
+from .nc_reader import load_nc
+from .to_blocks import write_blocks_arrow
+
+
+def _forward_fill_beached(frames: np.ndarray) -> None:
+    """Fem el beached persistent per partícula: al NC no és acumulatiu, i si llegim només cada hora
+    es podrien perdre les lectures intermitges on una partícula era beached. Un cop beached=1,
+    el mantenim 1 per a tots els passos següents (in-place)."""
+    num_steps, num_particles = frames.shape[0], frames.shape[1]
+    b = frames[:, :, 4]
+    for p in range(num_particles):
+        seen = False
+        for s in range(num_steps):
+            if b[s, p] == 1:
+                seen = True
+            elif seen:
+                b[s, p] = 1
+    frames[:, :, 4] = b
+
+
+def _subsample_to_hourly(
+    frames: np.ndarray,
+    num_steps: int,
+    num_particles: int,
+    release_steps: list[int],
+    time_ref_sec: np.ndarray,
+    time_start_iso: str,
+    time_end_iso: str,
+) -> tuple[np.ndarray, int, list[int]]:
+    """Keep one frame per hour (hora punta): step closest to each full hour. Returns (frames_hourly, new_num_steps, new_release_steps)."""
+    start_sec = np.datetime64(time_start_iso).astype("datetime64[s]").astype(np.float64)
+    end_sec = np.datetime64(time_end_iso).astype("datetime64[s]").astype(np.float64)
+    num_hours = max(1, int(round((end_sec - start_sec) / 3600)))
+    hourly_indices: list[int] = []
+    for h in range(num_hours):
+        hour_center = start_sec + h * 3600  # full hour (e.g. 07:00:00)
+        t_lo = hour_center
+        t_hi = start_sec + (h + 1) * 3600
+        # Step in this hour whose time is closest to the full hour
+        best_s: int | None = None
+        best_dt = float("inf")
+        for s in range(num_steps):
+            if np.isnan(time_ref_sec[s]):
+                continue
+            if t_lo <= time_ref_sec[s] < t_hi:
+                dt = abs(time_ref_sec[s] - hour_center)
+                if dt < best_dt:
+                    best_dt = dt
+                    best_s = s
+        if best_s is not None:
+            hourly_indices.append(best_s)
+    if not hourly_indices:
+        return frames, num_steps, release_steps
+    idx = np.array(hourly_indices, dtype=np.intp)
+    frames_hourly = frames[idx]
+    new_num_steps = len(hourly_indices)
+    # Map release_steps: for each particle, first hourly index >= its original release step
+    new_release_steps: list[int] = []
+    for p in range(num_particles):
+        r = release_steps[p]
+        i = 0
+        while i < new_num_steps and idx[i] < r:
+            i += 1
+        new_release_steps.append(min(i, new_num_steps - 1))
+    return frames_hourly, new_num_steps, new_release_steps
+
+
+def run_etl(
+    nc_path: str | Path,
+    out_dir: str | Path,
+    sim_id: str = "default",
+    write_json: bool = False,
+) -> dict:
+    """
+    Run full ETL: read .nc, optionally subsample to hourly, write blocks and metadata.
+
+    Returns metadata dict.
+    """
+    nc_path = Path(nc_path)
+    out_dir = Path(out_dir)
+    sim_dir = out_dir / "simulations" / sim_id
+
+    (
+        frames,
+        num_particles,
+        num_steps,
+        release_steps,
+        seed_names,
+        origins,
+        time_start_iso,
+        time_end_iso,
+        time_ref_sec,
+    ) = load_nc(str(nc_path))
+
+    # Beached: once a particle is beached it stays beached (so hourly sample doesn't miss it)
+    _forward_fill_beached(frames)
+
+    # Subsample to one frame per hour when we have a time reference
+    if (
+        time_ref_sec is not None
+        and time_start_iso is not None
+        and time_end_iso is not None
+        and np.any(np.isfinite(time_ref_sec))
+    ):
+        frames, num_steps, release_steps = _subsample_to_hourly(
+            frames, num_steps, num_particles, release_steps,
+            time_ref_sec, time_start_iso, time_end_iso,
+        )
+
+    metadata = write_blocks_arrow(
+        sim_dir,
+        frames,
+        num_particles,
+        num_steps,
+        release_steps,
+        seed_names,
+        origins,
+        write_json=write_json,
+        time_start_iso=time_start_iso,
+        time_end_iso=time_end_iso,
+    )
+    return metadata
--- a/backend/etl/schema.py
+++ b/backend/etl/schema.py
@ -0,0 +1,22 @@
+"""Constants and schema for trajectory ETL (NC → Arrow)."""
+
+BLOCK_SIZE = 24  # steps per block (same as frontend)
+
+# Default variable names to look for in NetCDF (first match wins)
+LON_NAMES = ("lon", "longitude", "x", "Lon")
+LAT_NAMES = ("lat", "latitude", "y", "Lat")
+U_NAMES = ("u", "u_vel", "velocity_x", "U")
+V_NAMES = ("v", "v_vel", "velocity_y", "V")
+BEACHED_NAMES = ("beached", "status", "mask", "beach")
+TIME_NAMES = ("time", "obs", "step", "t")
+
+# Arrow table schema for one block (frontend expects this)
+ARROW_SCHEMA = {
+    "step": "int32",
+    "particle_id": "int32",
+    "lon": "float32",
+    "lat": "float32",
+    "u": "float32",
+    "v": "float32",
+    "beached": "int8",
+}
--- a/backend/etl/to_blocks.py
+++ b/backend/etl/to_blocks.py
@ -0,0 +1,137 @@
+"""
+Write trajectory frames to block-wise Arrow files and metadata.json.
+Frontend expects: metadata.json, block_0.arrow, block_1.arrow, ...
+Arrow table per block: columns step, particle_id, lon, lat, u, v, beached; rows ordered by step then particle_id.
+"""
+
+from __future__ import annotations
+
+import json
+from pathlib import Path
+
+import numpy as np
+import pyarrow as pa
+
+from .schema import BLOCK_SIZE
+
+
+def build_accumulation(lons: np.ndarray, lats: np.ndarray, res: float = 0.1) -> list[list[float]]:
+    """Build accumulation grid cells for beached particles [lon_cell, lat_cell, count]."""
+    if lons.size == 0:
+        return []
+    cells: dict[tuple[int, int], int] = {}
+    for lo, la in zip(lons.ravel().tolist(), lats.ravel().tolist()):
+        if not np.isfinite(lo) or not np.isfinite(la):
+            continue
+        key = (round(lo / res), round(la / res))
+        cells[key] = cells.get(key, 0) + 1
+    return [[k[0] * res, k[1] * res, v] for k, v in cells.items()]
+
+
+def write_blocks_arrow(
+    out_dir: Path,
+    frames: np.ndarray,
+    num_particles: int,
+    num_steps: int,
+    release_steps: list[int],
+    seed_names: list[str],
+    origins: list[int],
+    write_json: bool = False,
+    time_start_iso: str | None = None,
+    time_end_iso: str | None = None,
+) -> dict:
+    """
+    Write blocks as Arrow IPC and metadata.json.
+    frames: (num_steps, num_particles, 5) with [lon, lat, u, v, beached].
+    Returns metadata dict for API.
+    """
+    out_dir = Path(out_dir)
+    out_dir.mkdir(parents=True, exist_ok=True)
+
+    # Remove any existing block files from a previous run (e.g. after re-ETL with fewer steps)
+    for p in out_dir.iterdir():
+        if p.is_file() and p.name.startswith("block_") and (p.suffix == ".arrow" or p.suffix == ".json"):
+            p.unlink()
+
+    num_blocks = (num_steps + BLOCK_SIZE - 1) // BLOCK_SIZE
+    metadata: dict = {
+        "num_particles": num_particles,
+        "num_steps": num_steps,
+        "num_blocks": num_blocks,
+        "block_size": BLOCK_SIZE,
+        "dt_hours": 1,
+        "seed_names": seed_names or [f"Origin {i}" for i in range(max(origins) + 1)] if origins else ["Default"],
+        "origins": origins,
+        "release_steps": release_steps,
+    }
+    if time_start_iso and time_end_iso:
+        metadata["time_start"] = time_start_iso
+        metadata["time_end"] = time_end_iso
+
+    for block_id in range(num_blocks):
+        step_start = block_id * BLOCK_SIZE
+        step_end = min(step_start + BLOCK_SIZE, num_steps)
+        chunk = frames[step_start:step_end]
+        n_steps_chunk = chunk.shape[0]
+
+        steps_list = []
+        particle_ids_list = []
+        lons_list = []
+        lats_list = []
+        u_list = []
+        v_list = []
+        beached_list = []
+
+        for step_idx in range(n_steps_chunk):
+            step_global = step_start + step_idx
+            for pid in range(num_particles):
+                row = chunk[step_idx, pid]
+                steps_list.append(step_global)
+                particle_ids_list.append(pid)
+                lons_list.append(float(row[0]))
+                lats_list.append(float(row[1]))
+                u_list.append(float(row[2]))
+                v_list.append(float(row[3]))
+                # beached: index 4; ensure 0/1 (source can be float)
+                b_val = row[4]
+                beached_list.append(1 if (float(b_val) > 0.5) else 0)
+
+        # Build columns; beached from numpy to ensure int8 layout for IPC
+        beached_np = np.array(beached_list, dtype=np.int8)
+        table = pa.table({
+            "step": pa.array(steps_list, type=pa.int32()),
+            "particle_id": pa.array(particle_ids_list, type=pa.int32()),
+            "lon": pa.array(lons_list, type=pa.float32()),
+            "lat": pa.array(lats_list, type=pa.float32()),
+            "u": pa.array(u_list, type=pa.float32()),
+            "v": pa.array(v_list, type=pa.float32()),
+            "beached": pa.array(beached_np),
+        })
+
+        arrow_path = out_dir / f"block_{block_id}.arrow"
+        with open(arrow_path, "wb") as f:
+            with pa.ipc.new_stream(f, table.schema) as writer:
+                writer.write_table(table)
+
+        if write_json:
+            frames_json = chunk.astype(float).tolist()
+            beached_mask = chunk[:, :, 4].astype(bool)
+            accumulation = []
+            for step_idx in range(n_steps_chunk):
+                b_lons = chunk[step_idx, beached_mask[step_idx], 0]
+                b_lats = chunk[step_idx, beached_mask[step_idx], 1]
+                accumulation.append(build_accumulation(b_lons, b_lats))
+            block_json = {
+                "block": block_id,
+                "step_start": step_start,
+                "step_end": step_end,
+                "frames": frames_json,
+                "accumulation": accumulation,
+            }
+            with open(out_dir / f"block_{block_id}.json", "w") as f:
+                json.dump(block_json, f, separators=(",", ":"))
+
+    with open(out_dir / "metadata.json", "w") as f:
+        json.dump(metadata, f, separators=(",", ":"))
+
+    return metadata
--- a/backend/generate_dummy_data.py
+++ b/backend/generate_dummy_data.py
@ -0,0 +1,323 @@
+"""
+Lagrangian particle trajectory simulator – compact block output.
+
+10 000 particles seeded along the Catalan coast, advected by a synthetic
+Western Mediterranean current field for 72 h (3 days).
+Output: 3 JSON blocks of 24 h each + a metadata file.
+Each block stores per-step arrays of [lon, lat, u, v, beached] per particle.
+Trails are reconstructed client-side for zero data duplication.
+"""
+
+import json
+import math
+import os
+import numpy as np
+
+DATA_DIR = os.path.join(os.path.dirname(__file__), "data")
+
+NUM_STEPS = 72
+DT_SECONDS = 3600
+DEG_PER_M_LAT = 1.0 / 111_320
+BLOCK_SIZE = 24  # steps per block
+PARTICLES_PER_SEED = 333
+
+JITTER_DEG = 0.008  # small spread so particles start in water near coast
+OFFSHORE_DEG = 0.012  # push seaward if initial position is on land
+
+SEED_POINTS = [
+    (3.21, 41.39), (2.82, 41.62), (2.17, 41.45), (1.82, 41.22),
+    (1.25, 41.12), (1.00, 40.95), (0.63, 40.62), (0.85, 40.72),
+    (3.12, 41.98), (3.19, 42.30), (2.82, 41.97), (2.07, 41.38),
+    (3.10, 41.77), (3.17, 41.70), (1.52, 41.08), (3.04, 41.87),
+    (0.75, 40.78), (2.93, 41.69), (1.60, 41.15), (2.40, 41.53),
+    (0.50, 40.55), (2.60, 41.57), (3.16, 42.12), (2.50, 41.55),
+    (1.40, 41.05), (3.05, 42.05), (2.92, 41.83), (1.15, 40.90),
+    (2.70, 41.64), (3.22, 42.20),
+]
+
+SEED_NAMES = [
+    "Barcelona", "Badalona", "Castelldefels", "Vilanova",
+    "Tarragona", "Cambrils", "Delta Ebre S", "Delta Ebre N",
+    "Roses", "Portbou", "L'Estartit", "Sitges",
+    "Blanes", "Lloret de Mar", "Salou", "Tossa de Mar",
+    "L'Ampolla", "St. Feliu Guíxols", "Torredembarra", "El Masnou",
+    "Alcanar", "Premià de Mar", "Cadaqués", "Vilassar de Mar",
+    "Altafulla", "L'Escala", "Palamós", "Miami Platja",
+    "Arenys de Mar", "Llançà",
+]
+
+# ── Land polygons ────────────────────────────────────────────────────────────
+
+IBERIAN_PENINSULA = [
+    (-2.0, 36.7), (-1.5, 36.8), (-0.5, 37.4), (0.0, 38.0),
+    (0.2, 38.8), (-0.2, 39.5), (0.0, 39.9), (0.2, 40.4),
+    (0.45, 40.5), (0.5, 40.65), (0.7, 40.75), (0.8, 40.85),
+    (0.9, 40.9), (1.0, 41.0), (1.2, 41.1), (1.5, 41.1),
+    (1.8, 41.2), (2.0, 41.3), (2.1, 41.35), (2.2, 41.4),
+    (2.5, 41.5), (2.8, 41.6), (2.9, 41.65), (3.0, 41.7),
+    (3.1, 41.8), (3.15, 41.9), (3.15, 42.0), (3.2, 42.1),
+    (3.2, 42.3), (3.25, 42.45), (3.05, 42.5), (2.5, 42.6),
+    (1.8, 42.7), (1.0, 42.75), (0.0, 42.7), (-1.0, 42.8),
+    (-2.0, 42.5), (-2.0, 36.7),
+]
+FRANCE_SOUTH = [
+    (3.05, 42.5), (3.25, 42.45), (3.3, 42.5), (3.5, 42.6),
+    (3.6, 43.0), (3.5, 43.2), (3.9, 43.3), (4.1, 43.4),
+    (4.5, 43.3), (4.8, 43.4), (5.0, 43.3), (5.5, 43.2),
+    (5.8, 43.1), (6.0, 43.1), (6.3, 43.15), (6.6, 43.0),
+    (7.0, 43.5), (7.5, 43.8), (7.5, 44.5), (6.0, 44.5),
+    (4.0, 44.0), (3.0, 43.5), (3.0, 42.8), (3.05, 42.5),
+]
+ITALY_WEST = [
+    (7.5, 43.8), (7.7, 43.8), (8.0, 43.9), (8.5, 44.0),
+    (9.0, 44.1), (9.5, 44.3), (10.0, 44.0), (10.0, 43.5),
+    (10.5, 43.0), (10.5, 42.5), (11.0, 42.0), (11.5, 41.5),
+    (12.0, 41.2), (12.5, 41.0), (13.0, 40.5), (13.5, 40.0),
+    (14.0, 39.5), (14.0, 38.5), (14.0, 44.5), (7.5, 44.5),
+    (7.5, 43.8),
+]
+SARDINIA = [
+    (8.1, 39.0), (8.3, 38.8), (8.5, 38.85), (8.8, 38.9),
+    (9.2, 39.0), (9.6, 39.2), (9.7, 39.8), (9.6, 40.2),
+    (9.5, 40.6), (9.2, 40.9), (8.8, 41.0), (8.3, 41.0),
+    (8.1, 40.8), (8.1, 40.4), (8.2, 39.8), (8.1, 39.0),
+]
+CORSICA = [
+    (8.6, 41.4), (8.8, 41.4), (9.2, 41.6), (9.4, 42.0),
+    (9.5, 42.4), (9.4, 42.8), (9.2, 43.0), (8.8, 42.7),
+    (8.6, 42.3), (8.6, 41.8), (8.6, 41.4),
+]
+MALLORCA = [
+    (2.3, 39.25), (2.7, 39.3), (3.1, 39.5), (3.4, 39.7),
+    (3.5, 39.85), (3.4, 39.95), (3.1, 39.95), (2.7, 39.9),
+    (2.4, 39.75), (2.3, 39.55), (2.3, 39.25),
+]
+MENORCA = [
+    (3.8, 39.8), (3.9, 39.82), (4.1, 39.95), (4.25, 40.05),
+    (4.1, 40.1), (3.85, 40.0), (3.8, 39.9), (3.8, 39.8),
+]
+IBIZA = [
+    (1.2, 38.8), (1.3, 38.82), (1.45, 38.9), (1.55, 39.0),
+    (1.5, 39.1), (1.35, 39.1), (1.2, 39.0), (1.15, 38.9),
+    (1.2, 38.8),
+]
+NORTH_AFRICA = [
+    (-2.0, 36.7), (-2.0, 35.0), (10.0, 35.0), (10.0, 37.0),
+    (9.5, 37.2), (9.0, 37.0), (8.5, 37.0), (8.0, 36.8),
+    (7.5, 36.9), (7.0, 37.0), (6.0, 37.0), (5.0, 36.8),
+    (4.0, 36.7), (3.0, 36.7), (2.0, 36.5), (1.0, 36.3),
+    (0.0, 35.8), (-1.0, 35.5), (-2.0, 36.7),
+]
+
+LAND_POLYGONS = [
+    IBERIAN_PENINSULA, FRANCE_SOUTH, ITALY_WEST,
+    SARDINIA, CORSICA, MALLORCA, MENORCA, IBIZA, NORTH_AFRICA,
+]
+
+
+def _pip(px, py, poly):
+    n = len(poly)
+    inside = False
+    j = n - 1
+    for i in range(n):
+        xi, yi = poly[i]
+        xj, yj = poly[j]
+        if ((yi > py) != (yj > py)) and (px < (xj - xi) * (py - yi) / (yj - yi) + xi):
+            inside = not inside
+        j = i
+    return inside
+
+
+def is_land(lon, lat):
+    for poly in LAND_POLYGONS:
+        if _pip(lon, lat, poly):
+            return True
+    return False
+
+
+# ── Current field (NW Mediterranean / Catalan coast, realistic) ───────────────
+
+# Typical surface currents: Northern Current ~0.1–0.25 m/s along coast (SW), weaker offshore
+BASE_SPEED_MS = 0.18  # m/s, main flow magnitude
+DIFFUSION_MS = 0.025  # turbulent fluctuation (m/s)
+
+def current_field(lon, lat, rng, t_frac):
+    # Main flow: SW along Catalan coast (negative v = south, slight negative u = west)
+    angle_deg = 215 + 8 * math.sin(2 * math.pi * t_frac)  # slow seasonal wobble
+    rad = math.radians(angle_deg)
+    u_base = BASE_SPEED_MS * math.cos(rad)
+    v_base = BASE_SPEED_MS * math.sin(rad)
+
+    # Coastal weakening: reduce speed when close to Iberian coast (lon < 2.5, lat 40–42.5)
+    dist_coast = 1.0
+    if lon < 3.2 and 40.4 < lat < 42.5:
+        dist_coast = max(0.15, (lon - 0.5) * 0.4 + (42.2 - lat) * 0.15)
+    factor = min(1.0, dist_coast)
+    u_main = u_base * factor
+    v_main = v_base * factor
+
+    # Weak cyclonic gyre east of Barcelona (3.5, 41.5), radius ~0.8 deg
+    cx, cy = 3.6, 41.4
+    dx, dy = lon - cx, lat - cy
+    r_deg = math.sqrt(dx * dx + dy * dy)
+    if r_deg < 0.9 and r_deg > 0.05:
+        gyre_speed = 0.06 * math.exp(-r_deg / 0.5)  # m/s
+        # tangential: (-dy, dx) for anticlockwise
+        u_gyre = -gyre_speed * (dy / r_deg)
+        v_gyre = gyre_speed * (dx / r_deg)
+    else:
+        u_gyre, v_gyre = 0.0, 0.0
+
+    # Small-scale turbulence (Gaussian, uncorrelated)
+    u_noise = rng.normal(0, DIFFUSION_MS)
+    v_noise = rng.normal(0, DIFFUSION_MS)
+
+    return (u_main + u_gyre + u_noise, v_main + v_gyre + v_noise)
+
+
+def advect_rk4(lon, lat, rng, t_frac):
+    cos_lat = math.cos(math.radians(lat))
+    dpm_lon = DEG_PER_M_LAT / max(cos_lat, 1e-6)
+
+    def vel(lo, la):
+        u, v = current_field(lo, la, rng, t_frac)
+        return u * DT_SECONDS * dpm_lon, v * DT_SECONDS * DEG_PER_M_LAT
+
+    k1 = vel(lon, lat)
+    k2 = vel(lon + k1[0] / 2, lat + k1[1] / 2)
+    k3 = vel(lon + k2[0] / 2, lat + k2[1] / 2)
+    k4 = vel(lon + k3[0], lat + k3[1])
+
+    new_lon = lon + (k1[0] + 2 * k2[0] + 2 * k3[0] + k4[0]) / 6
+    new_lat = lat + (k1[1] + 2 * k2[1] + 2 * k3[1] + k4[1]) / 6
+    u_f, v_f = current_field(new_lon, new_lat, rng, t_frac)
+    return new_lon, new_lat, u_f, v_f
+
+
+# ── Accumulation grid ────────────────────────────────────────────────────────
+
+ACCUM_RES = 0.1
+
+def build_accumulation(b_lons, b_lats):
+    if len(b_lons) == 0:
+        return []
+    cells: dict[tuple[int, int], int] = {}
+    for lo, la in zip(b_lons, b_lats):
+        key = (round(lo / ACCUM_RES), round(la / ACCUM_RES))
+        cells[key] = cells.get(key, 0) + 1
+    return [[k[0] * ACCUM_RES, k[1] * ACCUM_RES, v] for k, v in cells.items()]
+
+
+# ── Main ─────────────────────────────────────────────────────────────────────
+
+def generate():
+    os.makedirs(DATA_DIR, exist_ok=True)
+    rng = np.random.default_rng(42)
+
+    init_lons, init_lats, origins = [], [], []
+    for si, (slon, slat) in enumerate(SEED_POINTS):
+        for _ in range(PARTICLES_PER_SEED):
+            lon = slon + rng.uniform(-JITTER_DEG, JITTER_DEG)
+            lat = slat + rng.uniform(-JITTER_DEG, JITTER_DEG)
+            init_lons.append(lon)
+            init_lats.append(lat)
+            origins.append(si)
+
+    n = len(init_lons)
+    lons = np.array(init_lons, dtype=float)
+    lats = np.array(init_lats, dtype=float)
+
+    # Ensure every particle starts in water: push seaward (east/northeast) if on land
+    for i in range(n):
+        for _ in range(50):
+            if not is_land(lons[i], lats[i]):
+                break
+            lons[i] += rng.uniform(0, OFFSHORE_DEG)
+            lats[i] += rng.uniform(0, OFFSHORE_DEG * 0.5)
+    init_lons = lons.tolist()
+    init_lats = lats.tolist()
+
+    # Staggered release over first 24h for more realistic dispersion
+    release_steps = rng.integers(0, min(24, NUM_STEPS), size=n).tolist()
+    init_lons_arr = np.array(init_lons, dtype=float)
+    init_lats_arr = np.array(init_lats, dtype=float)
+
+    beached = np.zeros(n, dtype=bool)
+
+    # Collect ALL frames: frames[step] = [[lon, lat, u, v, beached], ...]
+    all_frames = []
+    all_accum = []
+
+    for step in range(NUM_STEPS):
+        t_frac = step / NUM_STEPS
+        frame = np.zeros((n, 5))
+
+        for i in range(n):
+            if step < release_steps[i]:
+                frame[i] = [init_lons_arr[i], init_lats_arr[i], 0.0, 0.0, 0]
+                continue
+            if step == release_steps[i]:
+                lons[i], lats[i] = init_lons_arr[i], init_lats_arr[i]
+
+            if not beached[i]:
+                nl, nla, u, v = advect_rk4(float(lons[i]), float(lats[i]), rng, t_frac)
+                if is_land(nl, nla):
+                    beached[i] = True
+                    u, v = 0.0, 0.0
+                else:
+                    lons[i], lats[i] = nl, nla
+                    frame[i] = [lons[i], lats[i], u, v, 0]
+                    continue
+
+            frame[i] = [lons[i], lats[i], 0.0, 0.0, 1 if beached[i] else 0]
+
+        all_frames.append(np.round(frame, 5).tolist())
+
+        b_mask = beached
+        accum = build_accumulation(lons[b_mask].tolist(), lats[b_mask].tolist())
+        all_accum.append(accum)
+
+        act = int(np.sum(~beached))
+        bch = int(np.sum(beached))
+        print(f"  Step {step:>2d}/{NUM_STEPS - 1}  |  active {act:>5d}  beached {bch:>5d}")
+
+    # Write blocks
+    num_blocks = NUM_STEPS // BLOCK_SIZE
+    for b in range(num_blocks):
+        s0 = b * BLOCK_SIZE
+        s1 = s0 + BLOCK_SIZE
+        block = {
+            "block": b,
+            "step_start": s0,
+            "step_end": s1,
+            "frames": all_frames[s0:s1],
+            "accumulation": all_accum[s0:s1],
+        }
+        path = os.path.join(DATA_DIR, f"block_{b}.json")
+        with open(path, "w") as f:
+            json.dump(block, f, separators=(",", ":"))
+        size_mb = os.path.getsize(path) / 1_048_576
+        print(f"  Block {b} ({s0}h-{s1 - 1}h) → {path}  [{size_mb:.1f} MB]")
+
+    # Metadata (release_steps: step at which each particle is released, 0..num_steps-1)
+    meta = {
+        "num_particles": n,
+        "num_steps": NUM_STEPS,
+        "num_blocks": num_blocks,
+        "block_size": BLOCK_SIZE,
+        "dt_hours": 1,
+        "seed_names": SEED_NAMES,
+        "origins": origins,
+        "release_steps": release_steps,
+    }
+    meta_path = os.path.join(DATA_DIR, "metadata.json")
+    with open(meta_path, "w") as f:
+        json.dump(meta, f, separators=(",", ":"))
+    print(f"  Metadata → {meta_path}")
+
+
+if __name__ == "__main__":
+    n = len(SEED_POINTS) * PARTICLES_PER_SEED
+    print(f"Simulating {n} particles for {NUM_STEPS} hours …")
+    generate()
+    print("Done.")
--- a/backend/main.py
+++ b/backend/main.py
@ -0,0 +1,168 @@
+"""FastAPI server – serves simulation blocks (JSON or Arrow) with gzip compression."""
+
+import json
+from pathlib import Path
+
+import pyarrow as pa
+from fastapi import FastAPI, HTTPException, Query
+from fastapi.middleware.cors import CORSMiddleware
+from fastapi.middleware.gzip import GZipMiddleware
+from fastapi.requests import Request
+from fastapi.responses import Response
+
+DATA_DIR = Path(__file__).parent / "data"
+
+app = FastAPI(title="Trajectory Viewer API")
+
+app.add_middleware(GZipMiddleware, minimum_size=1000)
+app.add_middleware(
+    CORSMiddleware,
+    allow_origins=["http://localhost:3000"],
+    allow_methods=["*"],
+    allow_headers=["*"],
+)
+
+# Cache by (sim_id, name) for metadata/json. Arrow not cached so ETL regeneration is visible without restart.
+_meta_cache: dict[tuple[str, str], dict] = {}
+
+
+def _sim_dir(sim_id: str) -> Path:
+    """Resolve data directory for a simulation. Backward compat: default can be data/ if no simulations/."""
+    sim_path = DATA_DIR / "simulations" / sim_id
+    if sim_path.exists():
+        return sim_path
+    if sim_id == "default" and (DATA_DIR / "metadata.json").exists():
+        return DATA_DIR
+    return sim_path
+
+
+def _load(sim_id: str, name: str) -> dict | None:
+    p = _sim_dir(sim_id) / name
+    if not p.exists():
+        return None
+    # Never cache metadata so regenerated ETL (e.g. time_start/time_end) is always served
+    if name == "metadata.json":
+        with open(p) as f:
+            return json.load(f)
+    key = (sim_id, name)
+    if key not in _meta_cache:
+        with open(p) as f:
+            _meta_cache[key] = json.load(f)
+    return _meta_cache[key]
+
+
+def _block_to_arrow(sim_id: str, block_id: int) -> bytes:
+    sim_path = _sim_dir(sim_id)
+    arrow_file = sim_path / f"block_{block_id}.arrow"
+    if arrow_file.exists():
+        with open(arrow_file, "rb") as f:
+            return f.read()
+    data = _load(sim_id, f"block_{block_id}.json")
+    if not data:
+        raise HTTPException(404, f"Block {block_id} not found")
+    frames = data["frames"]
+    step_start = data["step_start"]
+    n_particles = len(frames[0]) if frames else 0
+    steps = []
+    particle_ids = []
+    lons, lats, us, vs, beached = [], [], [], [], []
+    for step_idx, frame in enumerate(frames):
+        step_global = step_start + step_idx
+        for pid, row in enumerate(frame):
+            steps.append(step_global)
+            particle_ids.append(pid)
+            lons.append(row[0])
+            lats.append(row[1])
+            us.append(row[2])
+            vs.append(row[3])
+            beached.append(row[4])
+    table = pa.table({
+        "step": pa.array(steps, type=pa.int32()),
+        "particle_id": pa.array(particle_ids, type=pa.int32()),
+        "lon": pa.array(lons, type=pa.float32()),
+        "lat": pa.array(lats, type=pa.float32()),
+        "u": pa.array(us, type=pa.float32()),
+        "v": pa.array(vs, type=pa.float32()),
+        "beached": pa.array(beached, type=pa.int8()),
+    })
+    sink = pa.BufferOutputStream()
+    with pa.ipc.new_stream(sink, table.schema) as writer:
+        writer.write_table(table)
+    return sink.getvalue()
+
+
+@app.get("/api/simulations")
+def list_simulations():
+    """List available simulation IDs (for future N simulations)."""
+    out = []
+    if (DATA_DIR / "metadata.json").exists():
+        out.append({"id": "default", "name": "Default"})
+    sims_dir = DATA_DIR / "simulations"
+    if sims_dir.exists():
+        for d in sorted(sims_dir.iterdir()):
+            if d.is_dir() and (d / "metadata.json").exists():
+                out.append({"id": d.name, "name": d.name})
+    return out
+
+
+@app.get("/api/metadata")
+def metadata(sim: str = Query("default", description="Simulation ID")):
+    data = _load(sim, "metadata.json")
+    if not data:
+        raise HTTPException(
+            404,
+            "metadata.json not found – run generate_dummy_data.py or scripts/run_etl for this simulation",
+        )
+    return data
+
+
+@app.get("/api/block/{block_id}")
+def block(
+    block_id: int,
+    request: Request,
+    sim: str = Query("default", description="Simulation ID"),
+):
+    data = _load(sim, f"block_{block_id}.json")
+    if not data:
+        arrow_file = _sim_dir(sim) / f"block_{block_id}.arrow"
+        if not arrow_file.exists():
+            raise HTTPException(404, f"Block {block_id} not found")
+        if request.query_params.get("frames") == "false":
+            meta = _load(sim, "metadata.json")
+            if not meta:
+                raise HTTPException(404, "metadata.json not found")
+            num_blocks = meta["num_blocks"]
+            block_size = meta["block_size"]
+            step_start = block_id * block_size
+            step_end = min(step_start + block_size, meta["num_steps"])
+            return {
+                "block": block_id,
+                "step_start": step_start,
+                "step_end": step_end,
+                "accumulation": [],
+            }
+        raise HTTPException(
+            400,
+            "Block available only as Arrow; use /api/block/{id}/arrow (JSON not generated for this simulation)",
+        )
+    if request.query_params.get("frames") == "false":
+        return {
+            "block": data["block"],
+            "step_start": data["step_start"],
+            "step_end": data["step_end"],
+            "accumulation": data["accumulation"],
+        }
+    return data
+
+
+@app.get("/api/block/{block_id}/arrow")
+def block_arrow(
+    block_id: int,
+    sim: str = Query("default", description="Simulation ID"),
+):
+    buf = _block_to_arrow(sim, block_id)
+    return Response(
+        content=bytes(buf),
+        media_type="application/vnd.apache.arrow.stream",
+        headers={"Cache-Control": "public, max-age=3600"},
+    )
--- a/backend/requirements.txt
+++ b/backend/requirements.txt
@ -0,0 +1,6 @@
+fastapi
+uvicorn
+numpy
+pyarrow
+xarray
+netCDF4
--- a/backend/scripts/init.py
+++ b/backend/scripts/init.py
@ -0,0 +1 @@
+# CLI scripts
--- a/backend/scripts/run_etl.py
+++ b/backend/scripts/run_etl.py
@ -0,0 +1,57 @@
+#!/usr/bin/env python3
+"""
+CLI to run ETL: NetCDF trajectory file → Arrow blocks + metadata.
+
+Usage:
+  python -m scripts.run_etl path/to/trajectories.nc
+  python -m scripts.run_etl path/to/file.nc --sim-id my_run
+  python -m scripts.run_etl file.nc --out-dir /path/to/backend/data --write-json
+"""
+
+from __future__ import annotations
+
+import argparse
+from pathlib import Path
+
+
+def main():
+    parser = argparse.ArgumentParser(description="ETL: NetCDF trajectories → Arrow blocks")
+    parser.add_argument("nc_path", type=str, help="Path to input .nc file")
+    parser.add_argument(
+        "--out-dir",
+        type=str,
+        default=None,
+        help="Output base directory (default: backend/data)",
+    )
+    parser.add_argument(
+        "--sim-id",
+        type=str,
+        default="default",
+        help="Simulation ID (default: default)",
+    )
+    parser.add_argument(
+        "--write-json",
+        action="store_true",
+        help="Also write block_*.json (for backward compat)",
+    )
+    args = parser.parse_args()
+
+    if args.out_dir is None:
+        out_dir = Path(__file__).resolve().parent.parent / "data"
+    else:
+        out_dir = Path(args.out_dir)
+
+    from etl.pipeline import run_etl
+
+    nc_path = Path(args.nc_path)
+    if not nc_path.exists():
+        raise SystemExit(f"File not found: {nc_path}")
+
+    print(f"ETL: {nc_path} → {out_dir / 'simulations' / args.sim_id}")
+    meta = run_etl(nc_path, out_dir, sim_id=args.sim_id, write_json=args.write_json)
+    print(f"  num_particles={meta['num_particles']}, num_steps={meta['num_steps']}, num_blocks={meta['num_blocks']}")
+    print("Done.")
+
+
+if __name__ == "__main__":
+    main()
--- a/docs/Proposta_Requisits_Visor_Client.html
+++ b/docs/Proposta_Requisits_Visor_Client.html
@ -0,0 +1,219 @@
+<!DOCTYPE html>
+<html lang="ca">
+<head>
+  <meta charset="UTF-8">
+  <meta name="viewport" content="width=device-width, initial-scale=1.0">
+  <title>Requisits de programari — Visor de trajectòries lagrangianes</title>
+  <script src="https://cdn.jsdelivr.net/npm/mermaid@10/dist/mermaid.min.js"></script>
+  <style>
+    :root { --border: #e0e0e0; --muted: #555; --accent: #1a5f7a; --bg-note: #f8f9fa; --bg-capture: #fff9e6; }
+    body { font-family: 'Segoe UI', Calibri, sans-serif; max-width: 780px; margin: 2rem auto; padding: 0 1.5rem; line-height: 1.6; color: #1a1a1a; }
+    h1 { font-size: 1.6rem; font-weight: 700; border-bottom: 2px solid var(--border); padding-bottom: 0.4rem; margin: 0 0 0.25rem 0; }
+    h2 { font-size: 1.2rem; font-weight: 600; margin-top: 1.75rem; margin-bottom: 0.5rem; color: #333; }
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+    ul, ol { margin: 0.6rem 0; padding-left: 1.5rem; }
+    li { margin: 0.4rem 0; }
+    .meta { color: var(--muted); font-size: 0.9rem; margin-bottom: 1.25rem; }
+    .lead { font-size: 0.95rem; color: var(--muted); margin-bottom: 1.5rem; }
+    .toc { font-size: 0.9rem; background: var(--bg-note); border: 1px solid var(--border); border-radius: 6px; padding: 0.75rem 1rem; margin: 1.25rem 0; }
+    .toc ul { list-style: none; padding-left: 0; margin: 0; }
+    .toc li { margin: 0.2rem 0; }
+    .toc a { color: var(--accent); text-decoration: none; }
+    .toc a:hover { text-decoration: underline; }
+    .note { background: var(--bg-note); border-left: 4px solid var(--accent); padding: 0.75rem 1rem; margin: 1rem 0; font-size: 0.9rem; border-radius: 0 4px 4px 0; }
+    .capture-box { background: var(--bg-capture); border: 1px solid #e6d9b3; border-radius: 6px; padding: 0.85rem 1rem; margin: 1rem 0; font-size: 0.9rem; }
+    .capture-box h4 { margin: 0 0 0.5rem 0; font-size: 0.95rem; color: #7a6215; }
+    .capture-box ul { margin: 0.35rem 0 0 0; padding-left: 1.25rem; }
+    .req-id { font-family: monospace; font-size: 0.9em; color: var(--accent); }
+    a { color: var(--accent); }
+    a:hover { text-decoration: underline; }
+    hr { border: none; border-top: 1px solid var(--border); margin: 1.5rem 0; }
+    .mermaid { margin: 1.25rem 0; text-align: center; }
+    .diagram-caption { font-size: 0.85rem; color: var(--muted); margin-top: 0.25rem; font-style: italic; }
+    .section { margin-bottom: 1rem; }
+  </style>
+</head>
+<body>
+
+<h1>Requisits de programari — Visor de trajectòries lagrangianes</h1>
+<p class="meta"><strong>Document de requisits · Client</strong></p>
+
+<nav class="toc" aria-label="Contingut">
+  <strong>Índex</strong>
+  <ul>
+    <li>1. <a href="#intro">Introducció</a></li>
+    <li>2. <a href="#descripcio">Descripció general del producte</a></li>
+    <li>3. <a href="#actors">Actors i rols</a></li>
+    <li>4. <a href="#requisits">Requisits funcionals</a></li>
+    <li>5. <a href="#flux">Flux del sistema</a></li>
+    <li>6. <a href="#entregables">Entregables</a></li>
+    <li>7. <a href="#acceptacio">Criteris d'acceptació</a></li>
+    <li>8. <a href="#annexos">Annexos i referències</a></li>
+  </ul>
+</nav>
+
+<hr>
+
+<section class="section" id="intro">
+<h2>1. Introducció</h2>
+<h3>1.1 Objectiu del document</h3>
+<p>Aquest document defineix els requisits de programari del projecte <strong>Visor de trajectòries lagrangianes</strong>. Està dirigit al client i estableix l’abast funcional, els actors, els requisits i els criteris d’acceptació.</p>
+<h3>1.2 Abast</h3>
+<p>Inclou el visor web de visualització de trajectòries, l’àrea d’administració per a la càrrega i gestió de dades, el processament de fitxers NetCDF i el desplegament del conjunt. Queden fora d’abast els detalls d’arquitectura i implementació.</p>
+</section>
+
+<section class="section" id="descripcio">
+<h2>2. Descripció general del producte</h2>
+<ul>
+  <li>El producte és una <strong>aplicació web</strong> (visor) accessible des del navegador que permet visualitzar partícules contaminants (o similars) en moviment al Mediterrani occidental sobre un mapa.</li>
+  <li>Les partícules tenen origen en punts de la costa catalana, es dispersen amb els corrents durant un període definit (p. ex. 72 h) i, en arribar a la costa, queden encallades i s’acumulen. El visor permet identificar aquestes zones d’impacte de forma visual.</li>
+  <li>El mapa és interactiu (vistes 2D i 3D), amb animació temporal i controls per analitzar les dades. El producte està pensat per a l’anàlisi tècnica i per a la comunicació de resultats (reunions, informes).</li>
+</ul>
+</section>
+
+<section class="section" id="actors">
+<h2>3. Actors i rols</h2>
+<ul>
+  <li><strong>Administrador:</strong> usuari amb permisos per pujar fitxers de dades (format NetCDF) i per gestionar les simulacions (consultar llistat, eliminar i, si es pacta, actualitzar o substituir). És l’únic rol amb accés a aquestes operacions.</li>
+  <li><strong>Usuari final:</strong> usuari que accedeix al visor per consultar simulacions ja publicades. Pot seleccionar simulació, utilitzar el mapa i els controls d’animació, filtres i llegenda. No pot pujar ni eliminar dades.</li>
+</ul>
+</section>
+
+<section class="section" id="requisits">
+<h2>4. Requisits funcionals</h2>
+
+<h3>4.1 Administració i càrrega de dades</h3>
+<ul>
+  <li><span class="req-id">REQ-F-01</span> El sistema ha de permetre a l’administrador pujar fitxers NetCDF des d’una àrea d’administració dedicada.</li>
+  <li><span class="req-id">REQ-F-02</span> Els fitxers NetCDF hauran d’ajustar-se al format acordat (variables de longitud, latitud, velocitats, estat d’encallament, eixos de temps i partícules).</li>
+  <li><span class="req-id">REQ-F-03</span> El sistema ha de mostrar a l’administrador un llistat de simulacions disponibles (identificador, nom o data, segons implementació).</li>
+  <li><span class="req-id">REQ-F-04</span> El sistema ha de permetre a l’administrador eliminar simulacions. La simulació eliminada deixa d’estar disponible per als usuaris finals.</li>
+  <li><span class="req-id">REQ-F-05</span> Si es pacta, el sistema ha de permetre actualitzar o substituir fitxers existents sense crear una simulació nova.</li>
+  <li><span class="req-id">REQ-F-06</span> Un cop pujat un fitxer NetCDF, el sistema ha de validar-lo, processar-lo i deixar les dades disponibles per al visor sense intervenció manual addicional de l’administrador.</li>
+</ul>
+
+<h3>4.2 Visor — Mapa i visualització</h3>
+<ul>
+  <li><span class="req-id">REQ-F-07</span> El visor ha de mostrar un mapa base interactiu sobre el qual es dibuixen les trajectòries, amb zoom i desplaçament (pan).</li>
+  <li><span class="req-id">REQ-F-08</span> El visor ha de oferir diversos estils de mapa base (p. ex. clar, fosc) seleccionables per l’usuari.</li>
+  <li><span class="req-id">REQ-F-09</span> El visor ha de suportar visualització en 2D i 3D de les trajectòries.</li>
+  <li><span class="req-id">REQ-F-10</span> El visor ha de mostrar l’estela del moviment de cada partícula (traça temporal) per diferenciar les partícules en moviment de les encallades.</li>
+  <li><span class="req-id">REQ-F-11</span> El visor ha de assignar un color per punt d’origen (llançament) per permetre identificar l’origen de cada partícula.</li>
+  <li><span class="req-id">REQ-F-12</span> El visor ha de diferenciar visualment les partícules actives (en moviment) de les encallades (p. ex. mitjançant color o símbol).</li>
+</ul>
+
+<h3>4.3 Visor — Animació i temps</h3>
+<ul>
+  <li><span class="req-id">REQ-F-13</span> El visor ha de oferir controls de reproducció: iniciar (play) i aturar (pausa) l’animació temporal.</li>
+  <li><span class="req-id">REQ-F-14</span> El visor ha de oferir un control de velocitat de l’animació (múltiples graus, des de més lent fins a més ràpid).</li>
+  <li><span class="req-id">REQ-F-15</span> El visor ha de oferir un control (slider o equivalent) per desplaçar-se directament a un instant temporal concret sense reproduir l’animació completa.</li>
+  <li><span class="req-id">REQ-F-16</span> El visor ha de mostrar l’instant temporal actual (p. ex. “Dia 2 · 14:00” o data real si les dades la inclouen).</li>
+</ul>
+
+<h3>4.4 Visor — Filtres i capes</h3>
+<ul>
+  <li><span class="req-id">REQ-F-17</span> El visor ha de oferir un panell o menú de filtres per activar o desactivar capes visuals: esteles de moviment, partícules actives i partícules encallades.</li>
+  <li><span class="req-id">REQ-F-18</span> El visor ha de permetre canviar l’estil del mapa base des del panell de filtres o un menú equivalent.</li>
+</ul>
+
+<h3>4.5 Visor — Informació i ajuda</h3>
+<p>Informació contextual en passar el cursor sobre elements del mapa i llegenda per interpretar colors i estats.</p>
+<ul>
+  <li><span class="req-id">REQ-F-19</span> Tooltip sobre partícula: com a mínim origen i velocitat en aquell instant.</li>
+  <li><span class="req-id">REQ-F-20</span> Llegenda amb el significat dels colors, orígens i estats (actiu / encallat).</li>
+</ul>
+
+<h3>4.6 Visor — Navegació i simulacions</h3>
+<ul>
+  <li><span class="req-id">REQ-F-21</span> El visor ha de oferir una acció (p. ex. botó) per encuadrar totes les partícules visibles al mapa mitjançant zoom automàtic.</li>
+  <li><span class="req-id">REQ-F-22</span> Quan existeixin diverses simulacions, el visor ha de permetre seleccionar quina simulació visualitzar (desplegable, selector o paràmetre d’URL) i carregar les dades corresponents.</li>
+</ul>
+</section>
+
+<section class="section" id="flux">
+<h2>5. Flux del sistema</h2>
+
+<h3>5.1 Flux de dades</h3>
+<p>L’administrador puja fitxers NetCDF. El sistema els valida, els processa (incloent submostreig horari quan sigui aplicable) i genera les dades i metadades necessàries per al visor. Les simulacions queden disponibles per a tots els usuaris amb accés al visor. L’usuari final obre el visor, selecciona una simulació i utilitza els controls d’animació, filtres, tooltips i llegenda.</p>
+<div class="mermaid">
+flowchart LR
+    A[Administrador<br/>puja NetCDF] --> B[Sistema<br/>valida i processa]
+    B --> C[Simulacions<br/>disponibles]
+    C --> D[Usuari<br/>visualitza al visor]
+</div>
+<p class="diagram-caption">Figura 1 — Flux de dades.</p>
+
+<h3>5.2 Flux d’ús del visor</h3>
+<p>L’usuari accedeix al visor des del navegador, selecciona simulació (o se n’ofereix una per defecte), el mapa es carrega amb les trajectòries i l’usuari pot utilitzar zoom, desplaçament, controls de reproducció, filtres, tooltips i zoom a partícules.</p>
+<div class="mermaid">
+flowchart TB
+    O([Obrir visor]) --> T[Triar simulació]
+    T --> M[Mapa amb trajectòries]
+    M --> C{Controls}
+    C --> P[Play / Pausa / Velocitat]
+    C --> S[Slider temporal]
+    C --> F[Filtres i capes]
+    C --> Z[Zoom a partícules]
+    C --> L[Tooltips i llegenda]
+</div>
+<p class="diagram-caption">Figura 2 — Flux d’ús del visor.</p>
+</section>
+
+<section class="section" id="entregables">
+<h2>6. Entregables</h2>
+<ul>
+  <li><strong>Visor web:</strong> aplicació accessible des del navegador que implementa els requisits de les seccions 4.2 a 4.6 (mapa, animació, controls de temps, filtres, tooltips, llegenda).</li>
+  <li><strong>Àrea d’administració:</strong> interfície que implementa els requisits REQ-F-01 a REQ-F-06 (pujada de NetCDF, llistat, eliminació i, si s’acorda, actualització o substitució).</li>
+  <li><strong>Processament de dades:</strong> pipeline de validació i transformació dels fitxers NetCDF pujats per deixar les dades disponibles per al visor sense accions manuals addicionals.</li>
+  <li><strong>Documentació d’ús:</strong> instruccions per a l’administrador (càrrega i gestió de fitxers) i per a l’usuari final (ús del visor i controls), segons pacte.</li>
+  <li><strong>Desplegament:</strong> conjunt (visor, administració i processament) desplegat de forma reproducible (p. ex. contenidors), segons acord, per a la posada en marxa en l’entorn del client.</li>
+</ul>
+</section>
+
+<section class="section" id="acceptacio">
+<h2>7. Criteris d’acceptació</h2>
+<p>El projecte es donarà per acceptat quan es compleixin les condicions següents:</p>
+<ul>
+  <li>L’administrador pot pujar fitxers NetCDF en el format acordat i pot llistar i eliminar simulacions des de la interfície d’administració.</li>
+  <li>El visor mostra les trajectòries amb animació temporal i diferenciació clara entre partícules en moviment i encallades, i entre orígens (mitjançant colors i llegenda).</li>
+  <li>L’usuari final pot utilitzar sense errors els controls de reproducció (play, pausa, velocitat, slider), el panell de filtres i capes, els tooltips i la llegenda, la selecció de simulació i el zoom a partícules.</li>
+  <li>El rendiment del visor és acceptable amb el volum de partícules i passos temporals definits al projecte (reproducció fluida sense bloquejos evidents).</li>
+</ul>
+</section>
+
+<section class="section" id="annexos">
+<h2>8. Annexos i referències</h2>
+<p>Referències externes per contextualitzar el tipus de visualització. Les captures recomanades poden emprar-se per a documentació o presentacions del client.</p>
+
+<h3>8.1 Enllaços de referència</h3>
+<ul>
+  <li><a href="https://deck.gl" target="_blank" rel="noopener">deck.gl</a> — motor de visualització del visor.</li>
+  <li><a href="https://deck.gl/examples/trips-layer" target="_blank" rel="noopener">Trips Layer</a> — exemple de trajectòries animades amb estela; referència propera al comportament del visor.</li>
+  <li><a href="https://deck.gl/examples" target="_blank" rel="noopener">Exemples deck.gl</a>.</li>
+  <li><a href="https://maplibre.org" target="_blank" rel="noopener">MapLibre</a> — mapes base (sense clau d’API). <a href="https://maplibre.org/demos/" target="_blank" rel="noopener">Demos</a>.</li>
+  <li><a href="https://arrow.apache.org" target="_blank" rel="noopener">Apache Arrow</a> — format intern de dades (informatiu).</li>
+</ul>
+
+<h3>8.2 Captures recomanades per a documentació o presentació</h3>
+<div class="capture-box">
+<ul>
+  <li><strong>Captura principal:</strong> <a href="https://deck.gl/examples/trips-layer" target="_blank" rel="noopener">deck.gl — Trips Layer</a>. Obrir l’enllaç, activar l’animació (Play) i realitzar una captura de pantalla amb trajectòries amb estela i colors. Representa de forma adequada el tipus de visualització del producte.</li>
+  <li><strong>Captura opcional:</strong> <a href="https://maplibre.org/demos/" target="_blank" rel="noopener">MapLibre — Demos</a>. Seleccionar un estil de mapa (clar o fosc) i realitzar una captura per il·lustrar l’aspecte del mapa base del visor.</li>
+</ul>
+</div>
+</section>
+
+<hr>
+<p class="meta"><em>Document de requisits de programari. Per a consultes sobre requisits o abast, contactar amb el proveïdor.</em></p>
+
+<div class="note">
+  <strong>Ús del document en Word</strong><br>
+  Seleccioneu tot el contingut (Ctrl+A), copieu i enganxeu en un document Word. Per incloure els diagrames, obrir aquest fitxer al navegador, realitzar una captura de pantalla de cada diagrama (p. ex. Win+Shift+S) i enganxar-les al document. Per il·lustrar el visor, afegir la captura de <a href="https://deck.gl/examples/trips-layer" target="_blank" rel="noopener">Trips Layer</a> amb l’animació activa (secció 8.2).
+</div>
+
+<script>
+  mermaid.initialize({ startOnLoad: true, theme: 'neutral' });
+</script>
+</body>
+</html>
--- a/docs/Proposta_Requisits_Visor_Client.md
+++ b/docs/Proposta_Requisits_Visor_Client.md
@ -0,0 +1,172 @@
+# Requisits de programari — Visor de trajectòries lagrangianes
+
+**Document de requisits · Client**
+
+---
+
+## Índex
+
+1. [Introducció](#1-introducció)
+2. [Descripció general del producte](#2-descripció-general-del-producte)
+3. [Actors i rols](#3-actors-i-rols)
+4. [Requisits funcionals](#4-requisits-funcionals)
+5. [Flux del sistema](#5-flux-del-sistema)
+6. [Entregables](#6-entregables)
+7. [Criteris d'acceptació](#7-criteris-dacceptació)
+8. [Annexos i referències](#8-annexos-i-referències)
+
+---
+
+## 1. Introducció
+
+### 1.1 Objectiu del document
+
+Aquest document defineix els requisits de programari del projecte **Visor de trajectòries lagrangianes**. Està dirigit al client i estableix l'abast funcional, els actors, els requisits i els criteris d'acceptació.
+
+### 1.2 Abast
+
+Inclou el visor web de visualització de trajectòries, l'àrea d'administració per a la càrrega i gestió de dades, el processament de fitxers NetCDF i el desplegament del conjunt. Queden fora d'abast els detalls d'arquitectura i implementació.
+
+---
+
+## 2. Descripció general del producte
+
+- El producte és una **aplicació web** (visor) accessible des del navegador que permet visualitzar partícules contaminants (o similars) en moviment al Mediterrani occidental sobre un mapa.
+- Les partícules tenen origen en punts de la costa catalana, es dispersen amb els corrents durant un període definit (p. ex. 72 h) i, en arribar a la costa, queden encallades i s'acumulen. El visor permet identificar aquestes zones d'impacte de forma visual.
+- El mapa és interactiu (vistes 2D i 3D), amb animació temporal i controls per analitzar les dades. El producte està pensat per a l'anàlisi tècnica i per a la comunicació de resultats (reunions, informes).
+
+---
+
+## 3. Actors i rols
+
+- **Administrador:** usuari amb permisos per pujar fitxers de dades (format NetCDF) i per gestionar les simulacions (consultar llistat, eliminar i, si es pacta, actualitzar o substituir). És l'únic rol amb accés a aquestes operacions.
+- **Usuari final:** usuari que accedeix al visor per consultar simulacions ja publicades. Pot seleccionar simulació, utilitzar el mapa i els controls d'animació, filtres i llegenda. No pot pujar ni eliminar dades.
+
+---
+
+## 4. Requisits funcionals
+
+### 4.1 Administració i càrrega de dades
+
+- **REQ-F-01** El sistema ha de permetre a l'administrador pujar fitxers NetCDF des d'una àrea d'administració dedicada.
+- **REQ-F-02** Els fitxers NetCDF hauran d'ajustar-se al format acordat (variables de longitud, latitud, velocitats, estat d'encallament, eixos de temps i partícules).
+- **REQ-F-03** El sistema ha de mostrar a l'administrador un llistat de simulacions disponibles (identificador, nom o data, segons implementació).
+- **REQ-F-04** El sistema ha de permetre a l'administrador eliminar simulacions. La simulació eliminada deixa d'estar disponible per als usuaris finals.
+- **REQ-F-05** Si es pacta, el sistema ha de permetre actualitzar o substituir fitxers existents sense crear una simulació nova.
+- **REQ-F-06** Un cop pujat un fitxer NetCDF, el sistema ha de validar-lo, processar-lo i deixar les dades disponibles per al visor sense intervenció manual addicional de l'administrador.
+
+### 4.2 Visor — Mapa i visualització
+
+- **REQ-F-07** El visor ha de mostrar un mapa base interactiu sobre el qual es dibuixen les trajectòries, amb zoom i desplaçament (pan).
+- **REQ-F-08** El visor ha de oferir diversos estils de mapa base (p. ex. clar, fosc) seleccionables per l'usuari.
+- **REQ-F-09** El visor ha de suportar visualització en 2D i 3D de les trajectòries.
+- **REQ-F-10** El visor ha de mostrar l'estela del moviment de cada partícula (traça temporal) per diferenciar les partícules en moviment de les encallades.
+- **REQ-F-11** El visor ha d'assignar un color per punt d'origen (llançament) per permetre identificar l'origen de cada partícula.
+- **REQ-F-12** El visor ha de diferenciar visualment les partícules actives (en moviment) de les encallades (p. ex. mitjançant color o símbol).
+
+### 4.3 Visor — Animació i temps
+
+- **REQ-F-13** El visor ha d'oferir controls de reproducció: iniciar (play) i aturar (pausa) l'animació temporal.
+- **REQ-F-14** El visor ha d'oferir un control de velocitat de l'animació (múltiples graus, des de més lent fins a més ràpid).
+- **REQ-F-15** El visor ha d'oferir un control (slider o equivalent) per desplaçar-se directament a un instant temporal concret sense reproduir l'animació completa.
+- **REQ-F-16** El visor ha de mostrar l'instant temporal actual (p. ex. "Dia 2 · 14:00" o data real si les dades la inclouen).
+
+### 4.4 Visor — Filtres i capes
+
+- **REQ-F-17** El visor ha d'oferir un panell o menú de filtres per activar o desactivar capes visuals: esteles de moviment, partícules actives i partícules encallades.
+- **REQ-F-18** El visor ha de permetre canviar l'estil del mapa base des del panell de filtres o un menú equivalent.
+
+### 4.5 Visor — Informació i ajuda
+
+- **REQ-F-19** El visor ha de mostrar informació addicional (tooltip) en passar el cursor sobre una partícula: com a mínim origen i velocitat en aquell instant.
+- **REQ-F-20** El visor ha d'incloure una llegenda que expliqui el significat dels colors, orígens i estats (actiu / encallat) per a la interpretació per part de qualsevol usuari.
+
+### 4.6 Visor — Navegació i simulacions
+
+- **REQ-F-21** El visor ha d'oferir una acció (p. ex. botó) per encuadrar totes les partícules visibles al mapa mitjançant zoom automàtic.
+- **REQ-F-22** Quan existeixin diverses simulacions, el visor ha de permetre seleccionar quina simulació visualitzar (desplegable, selector o paràmetre d'URL) i carregar les dades corresponents.
+
+---
+
+## 5. Flux del sistema
+
+### 5.1 Flux de dades
+
+L'administrador puja fitxers NetCDF. El sistema els valida, els processa (incloent submostreig horari quan sigui aplicable) i genera les dades i metadades necessàries per al visor. Les simulacions queden disponibles per a tots els usuaris amb accés al visor. L'usuari final obre el visor, selecciona una simulació i utilitza els controls d'animació, filtres, tooltips i llegenda.
+
+```mermaid
+flowchart LR
+    A[Administrador<br/>puja NetCDF] --> B[Sistema<br/>valida i processa]
+    B --> C[Simulacions<br/>disponibles]
+    C --> D[Usuari<br/>visualitza al visor]
+```
+
+*Figura 1 — Flux de dades.*
+
+### 5.2 Flux d'ús del visor
+
+L'usuari accedeix al visor des del navegador, selecciona simulació (o se n'ofereix una per defecte), el mapa es carrega amb les trajectòries i l'usuari pot utilitzar zoom, desplaçament, controls de reproducció, filtres, tooltips i zoom a partícules.
+
+```mermaid
+flowchart TB
+    O([Obrir visor]) --> T[Triar simulació]
+    T --> M[Mapa amb trajectòries]
+    M --> C{Controls}
+    C --> P[Play / Pausa / Velocitat]
+    C --> S[Slider temporal]
+    C --> F[Filtres i capes]
+    C --> Z[Zoom a partícules]
+    C --> L[Tooltips i llegenda]
+```
+
+*Figura 2 — Flux d'ús del visor.*
+
+---
+
+## 6. Entregables
+
+- **Visor web:** aplicació accessible des del navegador que implementa els requisits de les seccions 4.2 a 4.6 (mapa, animació, controls de temps, filtres, tooltips, llegenda).
+- **Àrea d'administració:** interfície que implementa els requisits REQ-F-01 a REQ-F-06 (pujada de NetCDF, llistat, eliminació i, si s'acorda, actualització o substitució).
+- **Processament de dades:** pipeline de validació i transformació dels fitxers NetCDF pujats per deixar les dades disponibles per al visor sense accions manuals addicionals.
+- **Documentació d'ús:** instruccions per a l'administrador (càrrega i gestió de fitxers) i per a l'usuari final (ús del visor i controls), segons pacte.
+- **Desplegament:** conjunt (visor, administració i processament) desplegat de forma reproducible (p. ex. contenidors), segons acord, per a la posada en marxa en l'entorn del client.
+
+---
+
+## 7. Criteris d'acceptació
+
+El projecte es donarà per acceptat quan es compleixin les condicions següents:
+
+- L'administrador pot pujar fitxers NetCDF en el format acordat i pot llistar i eliminar simulacions des de la interfície d'administració.
+- El visor mostra les trajectòries amb animació temporal i diferenciació clara entre partícules en moviment i encallades, i entre orígens (mitjançant colors i llegenda).
+- L'usuari final pot utilitzar sense errors els controls de reproducció (play, pausa, velocitat, slider), el panell de filtres i capes, els tooltips i la llegenda, la selecció de simulació i el zoom a partícules.
+- El rendiment del visor és acceptable amb el volum de partícules i passos temporals definits al projecte (reproducció fluida sense bloquejos evidents).
+
+---
+
+## 8. Annexos i referències
+
+Referències externes per contextualitzar el tipus de visualització. Les captures recomanades poden emprar-se per a documentació o presentacions del client.
+
+### 8.1 Enllaços de referència
+
+- [deck.gl](https://deck.gl) — motor de visualització del visor.
+- [Trips Layer](https://deck.gl/examples/trips-layer) — exemple de trajectòries animades amb estela; referència propera al comportament del visor.
+- [Exemples deck.gl](https://deck.gl/examples).
+- [MapLibre](https://maplibre.org) — mapes base (sense clau d'API). [Demos](https://maplibre.org/demos/).
+- [Apache Arrow](https://arrow.apache.org) — format intern de dades (informatiu).
+
+### 8.2 Captures recomanades per a documentació o presentació
+
+- **Captura principal:** [deck.gl — Trips Layer](https://deck.gl/examples/trips-layer). Obrir l'enllaç, activar l'animació (Play) i realitzar una captura de pantalla amb trajectòries amb estela i colors. Representa de forma adequada el tipus de visualització del producte.
+- **Captura opcional:** [MapLibre — Demos](https://maplibre.org/demos/). Seleccionar un estil de mapa (clar o fosc) i realitzar una captura per il·lustrar l'aspecte del mapa base del visor.
+
+---
+
+*Document de requisits de programari. Per a consultes sobre requisits o abast, contactar amb el proveïdor.*
+
+---
+
+### Ús del document en Word
+
+Seleccioneu tot el contingut (Ctrl+A), copieu i enganxeu en un document Word. Per incloure els diagrames, obrir el fitxer HTML al navegador, realitzar una captura de pantalla de cada diagrama (p. ex. Win+Shift+S) i enganxar-les al document. Per il·lustrar el visor, afegir la captura de [Trips Layer](https://deck.gl/examples/trips-layer) amb l'animació activa (secció 8.2).
--- a/frontend/.gitignore
+++ b/frontend/.gitignore
@ -0,0 +1,41 @@
+# See https://help.github.com/articles/ignoring-files/ for more about ignoring files.
+
+# dependencies
+/node_modules
+/.pnp
+.pnp.*
+.yarn/*
+!.yarn/patches
+!.yarn/plugins
+!.yarn/releases
+!.yarn/versions
+
+# testing
+/coverage
+
+# next.js
+/.next/
+/out/
+
+# production
+/build
+
+# misc
+.DS_Store
+*.pem
+
+# debug
+npm-debug.log*
+yarn-debug.log*
+yarn-error.log*
+.pnpm-debug.log*
+
+# env files (can opt-in for committing if needed)
+.env*
+
+# vercel
+.vercel
+
+# typescript
+*.tsbuildinfo
+next-env.d.ts
--- a/frontend/README.md
+++ b/frontend/README.md
@ -0,0 +1,36 @@
+This is a [Next.js](https://nextjs.org) project bootstrapped with [`create-next-app`](https://nextjs.org/docs/app/api-reference/cli/create-next-app).
+
+## Getting Started
+
+First, run the development server:
+
+```bash
+npm run dev
+# or
+yarn dev
+# or
+pnpm dev
+# or
+bun dev
+```
+
+Open [http://localhost:3000](http://localhost:3000) with your browser to see the result.
+
+You can start editing the page by modifying `app/page.tsx`. The page auto-updates as you edit the file.
+
+This project uses [`next/font`](https://nextjs.org/docs/app/building-your-application/optimizing/fonts) to automatically optimize and load [Geist](https://vercel.com/font), a new font family for Vercel.
+
+## Learn More
+
+To learn more about Next.js, take a look at the following resources:
+
+- [Next.js Documentation](https://nextjs.org/docs) - learn about Next.js features and API.
+- [Learn Next.js](https://nextjs.org/learn) - an interactive Next.js tutorial.
+
+You can check out [the Next.js GitHub repository](https://github.com/vercel/next.js) - your feedback and contributions are welcome!
+
+## Deploy on Vercel
+
+The easiest way to deploy your Next.js app is to use the [Vercel Platform](https://vercel.com/new?utm_medium=default-template&filter=next.js&utm_source=create-next-app&utm_campaign=create-next-app-readme) from the creators of Next.js.
+
+Check out our [Next.js deployment documentation](https://nextjs.org/docs/app/building-your-application/deploying) for more details.
--- a/frontend/components.json
+++ b/frontend/components.json
@ -0,0 +1,23 @@
+{
+  "$schema": "https://ui.shadcn.com/schema.json",
+  "style": "new-york",
+  "rsc": true,
+  "tsx": true,
+  "tailwind": {
+    "config": "",
+    "css": "src/app/globals.css",
+    "baseColor": "neutral",
+    "cssVariables": true,
+    "prefix": ""
+  },
+  "iconLibrary": "lucide",
+  "rtl": false,
+  "aliases": {
+    "components": "@/components",
+    "utils": "@/lib/utils",
+    "ui": "@/components/ui",
+    "lib": "@/lib",
+    "hooks": "@/hooks"
+  },
+  "registries": {}
+}
--- a/frontend/eslint.config.mjs
+++ b/frontend/eslint.config.mjs
@ -0,0 +1,18 @@
+import { defineConfig, globalIgnores } from "eslint/config";
+import nextVitals from "eslint-config-next/core-web-vitals";
+import nextTs from "eslint-config-next/typescript";
+
+const eslintConfig = defineConfig([
+  ...nextVitals,
+  ...nextTs,
+  // Override default ignores of eslint-config-next.
+  globalIgnores([
+    // Default ignores of eslint-config-next:
+    ".next/**",
+    "out/**",
+    "build/**",
+    "next-env.d.ts",
+  ]),
+]);
+
+export default eslintConfig;
--- a/frontend/next.config.ts
+++ b/frontend/next.config.ts
@ -0,0 +1,7 @@
+import type { NextConfig } from "next";
+
+const nextConfig: NextConfig = {
+  /* config options here */
+};
+
+export default nextConfig;
--- a/frontend/package-lock.json
+++ b/frontend/package-lock.json
--- a/frontend/package.json
+++ b/frontend/package.json
@ -0,0 +1,41 @@
+{
+  "name": "frontend",
+  "version": "0.1.0",
+  "private": true,
+  "scripts": {
+    "dev": "next dev",
+    "build": "next build",
+    "start": "next start",
+    "lint": "eslint"
+  },
+  "dependencies": {
+    "@deck.gl/aggregation-layers": "^9.2.9",
+    "@deck.gl/geo-layers": "^9.2.9",
+    "@deck.gl/layers": "^9.2.9",
+    "@deck.gl/react": "^9.2.9",
+    "apache-arrow": "^21.1.0",
+    "class-variance-authority": "^0.7.1",
+    "clsx": "^2.1.1",
+    "deck.gl": "^9.2.9",
+    "lucide-react": "^0.575.0",
+    "maplibre-gl": "^5.18.0",
+    "next": "16.1.6",
+    "radix-ui": "^1.4.3",
+    "react": "19.2.3",
+    "react-dom": "19.2.3",
+    "react-map-gl": "^8.1.0",
+    "tailwind-merge": "^3.5.0"
+  },
+  "devDependencies": {
+    "@tailwindcss/postcss": "^4",
+    "@types/node": "^20",
+    "@types/react": "^19",
+    "@types/react-dom": "^19",
+    "eslint": "^9",
+    "eslint-config-next": "16.1.6",
+    "shadcn": "^3.8.5",
+    "tailwindcss": "^4",
+    "tw-animate-css": "^1.4.0",
+    "typescript": "^5"
+  }
+}
--- a/frontend/postcss.config.mjs
+++ b/frontend/postcss.config.mjs
@ -0,0 +1,7 @@
+const config = {
+  plugins: {
+    "@tailwindcss/postcss": {},
+  },
+};
+
+export default config;
--- a/frontend/public/file.svg
+++ b/frontend/public/file.svg
@ -0,0 +1 @@
+<svg fill="none" viewBox="0 0 16 16" xmlns="http://www.w3.org/2000/svg"><path d="M14.5 13.5V5.41a1 1 0 0 0-.3-.7L9.8.29A1 1 0 0 0 9.08 0H1.5v13.5A2.5 2.5 0 0 0 4 16h8a2.5 2.5 0 0 0 2.5-2.5m-1.5 0v-7H8v-5H3v12a1 1 0 0 0 1 1h8a1 1 0 0 0 1-1M9.5 5V2.12L12.38 5zM5.13 5h-.62v1.25h2.12V5zm-.62 3h7.12v1.25H4.5zm.62 3h-.62v1.25h7.12V11z" clip-rule="evenodd" fill="#666" fill-rule="evenodd"/></svg>
--- a/frontend/public/globe.svg
+++ b/frontend/public/globe.svg
@ -0,0 +1 @@
+<svg fill="none" xmlns="http://www.w3.org/2000/svg" viewBox="0 0 16 16"><g clip-path="url(#a)"><path fill-rule="evenodd" clip-rule="evenodd" d="M10.27 14.1a6.5 6.5 0 0 0 3.67-3.45q-1.24.21-2.7.34-.31 1.83-.97 3.1M8 16A8 8 0 1 0 8 0a8 8 0 0 0 0 16m.48-1.52a7 7 0 0 1-.96 0H7.5a4 4 0 0 1-.84-1.32q-.38-.89-.63-2.08a40 40 0 0 0 3.92 0q-.25 1.2-.63 2.08a4 4 0 0 1-.84 1.31zm2.94-4.76q1.66-.15 2.95-.43a7 7 0 0 0 0-2.58q-1.3-.27-2.95-.43a18 18 0 0 1 0 3.44m-1.27-3.54a17 17 0 0 1 0 3.64 39 39 0 0 1-4.3 0 17 17 0 0 1 0-3.64 39 39 0 0 1 4.3 0m1.1-1.17q1.45.13 2.69.34a6.5 6.5 0 0 0-3.67-3.44q.65 1.26.98 3.1M8.48 1.5l.01.02q.41.37.84 1.31.38.89.63 2.08a40 40 0 0 0-3.92 0q.25-1.2.63-2.08a4 4 0 0 1 .85-1.32 7 7 0 0 1 .96 0m-2.75.4a6.5 6.5 0 0 0-3.67 3.44 29 29 0 0 1 2.7-.34q.31-1.83.97-3.1M4.58 6.28q-1.66.16-2.95.43a7 7 0 0 0 0 2.58q1.3.27 2.95.43a18 18 0 0 1 0-3.44m.17 4.71q-1.45-.12-2.69-.34a6.5 6.5 0 0 0 3.67 3.44q-.65-1.27-.98-3.1" fill="#666"/></g><defs><clipPath id="a"><path fill="#fff" d="M0 0h16v16H0z"/></clipPath></defs></svg>
--- a/frontend/public/next.svg
+++ b/frontend/public/next.svg
@ -0,0 +1 @@
+<svg xmlns="http://www.w3.org/2000/svg" fill="none" viewBox="0 0 394 80"><path fill="#000" d="M262 0h68.5v12.7h-27.2v66.6h-13.6V12.7H262V0ZM149 0v12.7H94v20.4h44.3v12.6H94v21h55v12.6H80.5V0h68.7zm34.3 0h-17.8l63.8 79.4h17.9l-32-39.7 32-39.6h-17.9l-23 28.6-23-28.6zm18.3 56.7-9-11-27.1 33.7h17.8l18.3-22.7z"/><path fill="#000" d="M81 79.3 17 0H0v79.3h13.6V17l50.2 62.3H81Zm252.6-.4c-1 0-1.8-.4-2.5-1s-1.1-1.6-1.1-2.6.3-1.8 1-2.5 1.6-1 2.6-1 1.8.3 2.5 1a3.4 3.4 0 0 1 .6 4.3 3.7 3.7 0 0 1-3 1.8zm23.2-33.5h6v23.3c0 2.1-.4 4-1.3 5.5a9.1 9.1 0 0 1-3.8 3.5c-1.6.8-3.5 1.3-5.7 1.3-2 0-3.7-.4-5.3-1s-2.8-1.8-3.7-3.2c-.9-1.3-1.4-3-1.4-5h6c.1.8.3 1.6.7 2.2s1 1.2 1.6 1.5c.7.4 1.5.5 2.4.5 1 0 1.8-.2 2.4-.6a4 4 0 0 0 1.6-1.8c.3-.8.5-1.8.5-3V45.5zm30.9 9.1a4.4 4.4 0 0 0-2-3.3 7.5 7.5 0 0 0-4.3-1.1c-1.3 0-2.4.2-3.3.5-.9.4-1.6 1-2 1.6a3.5 3.5 0 0 0-.3 4c.3.5.7.9 1.3 1.2l1.8 1 2 .5 3.2.8c1.3.3 2.5.7 3.7 1.2a13 13 0 0 1 3.2 1.8 8.1 8.1 0 0 1 3 6.5c0 2-.5 3.7-1.5 5.1a10 10 0 0 1-4.4 3.5c-1.8.8-4.1 1.2-6.8 1.2-2.6 0-4.9-.4-6.8-1.2-2-.8-3.4-2-4.5-3.5a10 10 0 0 1-1.7-5.6h6a5 5 0 0 0 3.5 4.6c1 .4 2.2.6 3.4.6 1.3 0 2.5-.2 3.5-.6 1-.4 1.8-1 2.4-1.7a4 4 0 0 0 .8-2.4c0-.9-.2-1.6-.7-2.2a11 11 0 0 0-2.1-1.4l-3.2-1-3.8-1c-2.8-.7-5-1.7-6.6-3.2a7.2 7.2 0 0 1-2.4-5.7 8 8 0 0 1 1.7-5 10 10 0 0 1 4.3-3.5c2-.8 4-1.2 6.4-1.2 2.3 0 4.4.4 6.2 1.2 1.8.8 3.2 2 4.3 3.4 1 1.4 1.5 3 1.5 5h-5.8z"/></svg>
--- a/frontend/public/vercel.svg
+++ b/frontend/public/vercel.svg
@ -0,0 +1 @@
+<svg fill="none" xmlns="http://www.w3.org/2000/svg" viewBox="0 0 1155 1000"><path d="m577.3 0 577.4 1000H0z" fill="#fff"/></svg>
--- a/frontend/public/window.svg
+++ b/frontend/public/window.svg
@ -0,0 +1 @@
+<svg fill="none" xmlns="http://www.w3.org/2000/svg" viewBox="0 0 16 16"><path fill-rule="evenodd" clip-rule="evenodd" d="M1.5 2.5h13v10a1 1 0 0 1-1 1h-11a1 1 0 0 1-1-1zM0 1h16v11.5a2.5 2.5 0 0 1-2.5 2.5h-11A2.5 2.5 0 0 1 0 12.5zm3.75 4.5a.75.75 0 1 0 0-1.5.75.75 0 0 0 0 1.5M7 4.75a.75.75 0 1 1-1.5 0 .75.75 0 0 1 1.5 0m1.75.75a.75.75 0 1 0 0-1.5.75.75 0 0 0 0 1.5" fill="#666"/></svg>
--- a/frontend/src/app/favicon.ico
+++ b/frontend/src/app/favicon.ico
--- a/frontend/src/app/globals.css
+++ b/frontend/src/app/globals.css
@ -0,0 +1,149 @@
+@import "tailwindcss";
+@import "shadcn/tailwind.css";
+
+@custom-variant dark (&:is(.dark *));
+
+@theme inline {
+  --font-sans: var(--font-inter);
+  --color-sidebar-ring: var(--sidebar-ring);
+  --color-sidebar-border: var(--sidebar-border);
+  --color-sidebar-accent-foreground: var(--sidebar-accent-foreground);
+  --color-sidebar-accent: var(--sidebar-accent);
+  --color-sidebar-primary-foreground: var(--sidebar-primary-foreground);
+  --color-sidebar-primary: var(--sidebar-primary);
+  --color-sidebar-foreground: var(--sidebar-foreground);
+  --color-sidebar: var(--sidebar);
+  --color-chart-5: var(--chart-5);
+  --color-chart-4: var(--chart-4);
+  --color-chart-3: var(--chart-3);
+  --color-chart-2: var(--chart-2);
+  --color-chart-1: var(--chart-1);
+  --color-ring: var(--ring);
+  --color-input: var(--input);
+  --color-border: var(--border);
+  --color-destructive: var(--destructive);
+  --color-accent-foreground: var(--accent-foreground);
+  --color-accent: var(--accent);
+  --color-muted-foreground: var(--muted-foreground);
+  --color-muted: var(--muted);
+  --color-secondary-foreground: var(--secondary-foreground);
+  --color-secondary: var(--secondary);
+  --color-primary-foreground: var(--primary-foreground);
+  --color-primary: var(--primary);
+  --color-popover-foreground: var(--popover-foreground);
+  --color-popover: var(--popover);
+  --color-card-foreground: var(--card-foreground);
+  --color-card: var(--card);
+  --color-foreground: var(--foreground);
+  --color-background: var(--background);
+  --radius-sm: calc(var(--radius) - 4px);
+  --radius-md: calc(var(--radius) - 2px);
+  --radius-lg: var(--radius);
+  --radius-xl: calc(var(--radius) + 4px);
+  --radius-2xl: calc(var(--radius) + 8px);
+  --radius-3xl: calc(var(--radius) + 12px);
+  --radius-4xl: calc(var(--radius) + 16px);
+}
+
+html,
+body {
+  height: 100%;
+  margin: 0;
+  padding: 0;
+  overflow: hidden;
+  background: #0a0a0f;
+}
+
+input[type="range"] {
+  height: 6px;
+}
+
+input[type="range"]::-webkit-slider-thumb {
+  width: 14px;
+  height: 14px;
+}
+
+:root {
+  --radius: 0.625rem;
+  --background: oklch(1 0 0);
+  --foreground: oklch(0.145 0 0);
+  --card: oklch(1 0 0);
+  --card-foreground: oklch(0.145 0 0);
+  --popover: oklch(1 0 0);
+  --popover-foreground: oklch(0.145 0 0);
+  --primary: oklch(0.205 0 0);
+  --primary-foreground: oklch(0.985 0 0);
+  --secondary: oklch(0.97 0 0);
+  --secondary-foreground: oklch(0.205 0 0);
+  --muted: oklch(0.97 0 0);
+  --muted-foreground: oklch(0.556 0 0);
+  --accent: oklch(0.97 0 0);
+  --accent-foreground: oklch(0.205 0 0);
+  --destructive: oklch(0.577 0.245 27.325);
+  --border: oklch(0.922 0 0);
+  --input: oklch(0.922 0 0);
+  --ring: oklch(0.708 0 0);
+  --chart-1: oklch(0.646 0.222 41.116);
+  --chart-2: oklch(0.6 0.118 184.704);
+  --chart-3: oklch(0.398 0.07 227.392);
+  --chart-4: oklch(0.828 0.189 84.429);
+  --chart-5: oklch(0.769 0.188 70.08);
+  --sidebar: oklch(0.985 0 0);
+  --sidebar-foreground: oklch(0.145 0 0);
+  --sidebar-primary: oklch(0.205 0 0);
+  --sidebar-primary-foreground: oklch(0.985 0 0);
+  --sidebar-accent: oklch(0.97 0 0);
+  --sidebar-accent-foreground: oklch(0.205 0 0);
+  --sidebar-border: oklch(0.922 0 0);
+  --sidebar-ring: oklch(0.708 0 0);
+}
+
+.dark {
+  --background: oklch(0.145 0 0);
+  --foreground: oklch(0.985 0 0);
+  --card: oklch(0.205 0 0);
+  --card-foreground: oklch(0.985 0 0);
+  --popover: oklch(0.205 0 0);
+  --popover-foreground: oklch(0.985 0 0);
+  --primary: oklch(0.922 0 0);
+  --primary-foreground: oklch(0.205 0 0);
+  --secondary: oklch(0.269 0 0);
+  --secondary-foreground: oklch(0.985 0 0);
+  --muted: oklch(0.269 0 0);
+  --muted-foreground: oklch(0.708 0 0);
+  --accent: oklch(0.269 0 0);
+  --accent-foreground: oklch(0.985 0 0);
+  --destructive: oklch(0.704 0.191 22.216);
+  --border: oklch(1 0 0 / 10%);
+  --input: oklch(1 0 0 / 15%);
+  --ring: oklch(0.556 0 0);
+  --chart-1: oklch(0.488 0.243 264.376);
+  --chart-2: oklch(0.696 0.17 162.48);
+  --chart-3: oklch(0.769 0.188 70.08);
+  --chart-4: oklch(0.627 0.265 303.9);
+  --chart-5: oklch(0.645 0.246 16.439);
+  --sidebar: oklch(0.205 0 0);
+  --sidebar-foreground: oklch(0.985 0 0);
+  --sidebar-primary: oklch(0.488 0.243 264.376);
+  --sidebar-primary-foreground: oklch(0.985 0 0);
+  --sidebar-accent: oklch(0.269 0 0);
+  --sidebar-accent-foreground: oklch(0.985 0 0);
+  --sidebar-border: oklch(1 0 0 / 10%);
+  --sidebar-ring: oklch(0.556 0 0);
+}
+
+@layer base {
+  * {
+    @apply border-border outline-ring/50;
+  }
+  body {
+    @apply bg-background text-foreground;
+  }
+  button,
+  [role="button"],
+  a,
+  [type="button"],
+  [type="submit"] {
+    cursor: pointer;
+  }
+}
--- a/frontend/src/app/layout.tsx
+++ b/frontend/src/app/layout.tsx
@ -0,0 +1,23 @@
+import type { Metadata } from "next";
+import { Inter } from "next/font/google";
+import "./globals.css";
+
+const inter = Inter({ subsets: ["latin"], variable: "--font-inter" });
+
+export const metadata: Metadata = {
+  title: "Simulador de Contaminació Marina",
+  description:
+    "Visor de trajectòries lagrangianes de partícules contaminants al Mediterrani occidental",
+};
+
+export default function RootLayout({
+  children,
+}: Readonly<{ children: React.ReactNode }>) {
+  return (
+    <html lang="ca" className="dark">
+      <body className={`${inter.variable} font-sans antialiased bg-background text-foreground`}>
+        {children}
+      </body>
+    </html>
+  );
+}
--- a/frontend/src/app/page.tsx
+++ b/frontend/src/app/page.tsx
@ -0,0 +1,9 @@
+import TrajectoryMap from "@/components/TrajectoryMap";
+
+export default function Home() {
+  return (
+    <main className="w-screen h-screen">
+      <TrajectoryMap />
+    </main>
+  );
+}
--- a/frontend/src/components/IntroDialog.tsx
+++ b/frontend/src/components/IntroDialog.tsx
@ -0,0 +1,126 @@
+"use client";
+
+import { useState } from "react";
+import {
+  Dialog,
+  DialogContent,
+  DialogDescription,
+  DialogFooter,
+  DialogHeader,
+  DialogTitle,
+} from "@/components/ui/dialog";
+import { Button } from "@/components/ui/button";
+import { Waves, MapPin, Keyboard } from "lucide-react";
+
+const INTRO_SKIP_KEY = "trajectories_intro_skip";
+
+interface IntroDialogProps {
+  open: boolean;
+  onOpenChange: (open: boolean) => void;
+}
+
+export function IntroDialog({ open, onOpenChange }: IntroDialogProps) {
+  const [dontShowAgain, setDontShowAgain] = useState(false);
+
+  const handleStart = () => {
+    if (dontShowAgain && typeof window !== "undefined") {
+      localStorage.setItem(INTRO_SKIP_KEY, "true");
+    }
+    onOpenChange(false);
+  };
+
+  return (
+    <Dialog open={open} onOpenChange={onOpenChange}>
+      <DialogContent className="sm:max-w-md rounded-2xl border-slate-600 bg-slate-800/98 shadow-2xl backdrop-blur-sm text-left">
+        <DialogHeader className="space-y-3">
+          <DialogTitle className="flex items-center gap-3 text-white text-xl">
+            <span className="flex size-12 items-center justify-center rounded-2xl bg-gradient-to-br from-teal-400 to-teal-600 text-slate-900 shadow-lg shadow-teal-500/30">
+              <Waves className="size-6" />
+            </span>
+            <span>
+              Visualitzador de trajectòries
+              <span className="block text-sm font-normal text-slate-400 mt-0.5">
+                Mediterrània NW · UPC
+              </span>
+            </span>
+          </DialogTitle>
+          <DialogDescription asChild>
+            <div className="text-slate-400 space-y-3 text-sm leading-relaxed">
+              <p>
+                Aquesta eina mostra una{" "}
+                <strong className="text-slate-300">simulació lagrangiana</strong>{" "}
+                de partícules al Mediterrani nord-occidental: alliberades des de la
+                costa catalana i advectades per un camp de corrents. Les dades es
+                mostren <strong className="text-slate-300">cada hora</strong> durant
+                diversos dies.
+              </p>
+              <p>
+                Metodologia compatible amb{" "}
+                <a
+                  href="https://oceanparcels.org/"
+                  target="_blank"
+                  rel="noopener noreferrer"
+                  className="text-teal-400 hover:text-teal-300 underline underline-offset-2"
+                >
+                  Ocean Parcels
+                </a>
+                : partícules passives; les que toquen costa es marquen com a{" "}
+                <strong className="text-slate-300">beached</strong>.
+              </p>
+            </div>
+          </DialogDescription>
+        </DialogHeader>
+
+        <div className="grid grid-cols-2 gap-3">
+          <div className="rounded-xl border border-slate-600 bg-slate-700/50 p-3 flex items-start gap-2">
+            <span className="size-3 rounded-full bg-teal-400 shrink-0 mt-1 shadow-sm shadow-teal-400/40" />
+            <div>
+              <p className="font-medium text-slate-200 text-sm">Actives</p>
+              <p className="text-xs text-slate-500">A l’aigua</p>
+            </div>
+          </div>
+          <div className="rounded-xl border border-slate-600 bg-slate-700/50 p-3 flex items-start gap-2">
+            <MapPin className="size-4 shrink-0 mt-0.5 text-red-400" />
+            <div>
+              <p className="font-medium text-slate-200 text-sm">Beached</p>
+              <p className="text-xs text-slate-500">A la costa</p>
+            </div>
+          </div>
+        </div>
+
+        <div className="rounded-xl border border-slate-600 bg-slate-700/30 px-3 py-2 flex items-center gap-2 text-xs text-slate-500">
+          <Keyboard className="size-3.5 shrink-0" />
+          <span>
+            <kbd className="px-1.5 py-0.5 rounded bg-slate-600 text-slate-300 font-mono text-[10px]">←</kbd>{" "}
+            <kbd className="px-1.5 py-0.5 rounded bg-slate-600 text-slate-300 font-mono text-[10px]">→</kbd>{" "}
+            una hora · Espai: play/pausa
+          </span>
+        </div>
+
+        <label className="flex items-center gap-2 cursor-pointer text-sm text-slate-500 hover:text-slate-400 transition-colors">
+          <input
+            type="checkbox"
+            checked={dontShowAgain}
+            onChange={(e) => setDontShowAgain(e.target.checked)}
+            className="rounded border-slate-500 bg-slate-700 text-teal-500 focus:ring-teal-500/50"
+          />
+          <span>No tornar a mostrar</span>
+        </label>
+
+        <DialogFooter className="flex flex-row justify-end gap-2 sm:gap-2">
+          <Button
+            onClick={handleStart}
+            className="rounded-xl bg-teal-500 px-6 hover:bg-teal-400 text-slate-900 font-semibold shadow-lg shadow-teal-500/25"
+          >
+            Començar
+          </Button>
+        </DialogFooter>
+      </DialogContent>
+    </Dialog>
+  );
+}
+
+export function shouldShowIntro(): boolean {
+  if (typeof window === "undefined") return true;
+  return localStorage.getItem(INTRO_SKIP_KEY) !== "true";
+}
--- a/frontend/src/components/LoadingCard.tsx
+++ b/frontend/src/components/LoadingCard.tsx
@ -0,0 +1,33 @@
+"use client";
+
+import { Card, CardContent, CardDescription, CardHeader, CardTitle } from "@/components/ui/card";
+import { Progress } from "@/components/ui/progress";
+import type { Meta } from "@/types/trajectory";
+
+interface LoadingCardProps {
+  meta: Meta | null;
+  loadProgress: number;
+}
+
+export function LoadingCard({ meta, loadProgress }: LoadingCardProps) {
+  return (
+    <div className="fixed inset-0 z-40 flex flex-col items-center justify-center bg-slate-800">
+      <Card className="w-full max-w-sm rounded-2xl border-slate-600 bg-slate-800 shadow-2xl">
+        <CardHeader>
+          <CardTitle className="text-center text-white">
+            Loading trajectories…
+          </CardTitle>
+          <CardDescription className="text-center text-slate-400">
+            {meta
+              ? `${meta.num_particles.toLocaleString()} particles · ${meta.num_steps}h`
+              : "Connecting…"}
+          </CardDescription>
+        </CardHeader>
+        <CardContent className="space-y-4">
+          <Progress value={loadProgress} className="h-2 rounded-full" />
+          <p className="text-center text-sm text-slate-400">{loadProgress}%</p>
+        </CardContent>
+      </Card>
+    </div>
+  );
+}
--- a/frontend/src/components/MapHeader.tsx
+++ b/frontend/src/components/MapHeader.tsx
@ -0,0 +1,328 @@
+"use client";
+
+import { useRef } from "react";
+import { Layers, Filter, ChevronDown, Info, Map as MapIcon } from "lucide-react";
+import { Button } from "@/components/ui/button";
+import { Switch } from "@/components/ui/switch";
+import { Label } from "@/components/ui/label";
+import { BASEMAPS, HEADER_THEMES } from "@/lib/constants";
+import { useClickOutside } from "@/hooks/useClickOutside";
+
+interface MapHeaderProps {
+  basemapId: string;
+  setBasemapId: (id: string) => void;
+  day: number;
+  hour: number;
+  /** When set, show calendar date in header (e.g. "27 Aug 06:00") */
+  dateLabel?: string | null;
+  activeN: number;
+  beachedN: number;
+  filtersOpen: boolean;
+  setFiltersOpen: (v: boolean) => void;
+  infoOpen: boolean;
+  setInfoOpen: (v: boolean) => void;
+  showTrails: boolean;
+  setShowTrails: (v: boolean) => void;
+  showActiveParticles: boolean;
+  setShowActiveParticles: (v: boolean) => void;
+  showBeachedParticles: boolean;
+  setShowBeachedParticles: (v: boolean) => void;
+}
+
+export function MapHeader({
+  basemapId,
+  setBasemapId,
+  day,
+  hour,
+  dateLabel = null,
+  activeN,
+  beachedN,
+  filtersOpen,
+  setFiltersOpen,
+  infoOpen,
+  setInfoOpen,
+  showTrails,
+  setShowTrails,
+  showActiveParticles,
+  setShowActiveParticles,
+  showBeachedParticles,
+  setShowBeachedParticles,
+}: MapHeaderProps) {
+  const filtersRef = useRef<HTMLDivElement>(null);
+  const infoRef = useRef<HTMLDivElement>(null);
+  useClickOutside(filtersRef, filtersOpen, () => setFiltersOpen(false));
+  useClickOutside(infoRef, infoOpen, () => setInfoOpen(false));
+
+  const theme = HEADER_THEMES[basemapId] ?? HEADER_THEMES.dark;
+
+  return (
+    <header
+      className={`absolute left-0 right-0 top-0 z-10 flex items-center justify-between gap-6 px-5 py-3 shadow-xl backdrop-blur-xl border-b ${theme.bg} ${theme.border} ${theme.text}`}
+    >
+      <div className="flex items-center gap-6 min-w-0">
+        <div className="flex items-center gap-3 shrink-0">
+          <div
+            className={`flex size-9 items-center justify-center rounded-lg ring-1 ${theme.accentMuted} ${theme.accent}`}
+          >
+            <Layers className="size-5" />
+          </div>
+          <div>
+            <h1
+              className={`text-base font-bold tracking-tight leading-tight ${theme.text}`}
+            >
+              Lagrangian trajectories · UPC
+            </h1>
+            <p className={`text-[11px] font-medium ${theme.subtitle}`}>
+              Catalan coast · 72 h
+            </p>
+          </div>
+        </div>
+        <div className="hidden sm:block h-8 w-px bg-slate-600/80 shrink-0" />
+        <div className="flex items-center gap-4 shrink-0">
+          <div
+            className={`flex items-center gap-2 rounded-lg px-3 py-1.5 border ${theme.card}`}
+          >
+            <span
+              className={`text-[11px] uppercase tracking-wider font-medium ${theme.subtitle}`}
+            >
+              Time
+            </span>
+            <span
+              className={`text-sm font-semibold tabular-nums ${theme.text}`}
+            >
+              {dateLabel ?? `Day ${day} · ${hour.toString().padStart(2, "0")}:00`}
+            </span>
+          </div>
+          <div className="flex items-center gap-2">
+            <div className="flex items-center gap-1.5 rounded-md bg-teal-500/10 px-2.5 py-1 border border-teal-500/20">
+              <span className="size-2 rounded-full bg-teal-400 shrink-0" />
+              <span className="text-sm font-semibold text-teal-300 tabular-nums">
+                {activeN.toLocaleString()}
+              </span>
+              <span className={`text-[11px] ${theme.subtitle}`}>active</span>
+            </div>
+            <div className="flex items-center gap-1.5 rounded-md bg-red-500/10 px-2.5 py-1 border border-red-500/20">
+              <span className="size-2 rounded-full bg-red-500 shrink-0" />
+              <span className="text-sm font-semibold text-red-400 tabular-nums">
+                {beachedN.toLocaleString()}
+              </span>
+              <span className={`text-[11px] ${theme.subtitle}`}>beached</span>
+            </div>
+          </div>
+        </div>
+      </div>
+      <div className="flex items-center gap-2 shrink-0" ref={filtersRef}>
+        <div className="relative" ref={infoRef}>
+          <Button
+            variant="ghost"
+            size="sm"
+            className={`gap-2 rounded-lg px-3.5 py-2.5 text-sm font-medium transition-all ${
+              infoOpen
+                ? "bg-teal-500/15 text-teal-300 border border-teal-500/40"
+                : `border ${theme.card} hover:opacity-90 ${theme.text}`
+            }`}
+            onClick={(e) => {
+              e.stopPropagation();
+              setInfoOpen(!infoOpen);
+            }}
+            aria-label="About this project"
+            aria-expanded={infoOpen}
+          >
+            <Info className="size-4" />
+            Info
+          </Button>
+          {infoOpen && (
+            <div className="absolute right-0 top-full z-50 mt-2 w-96 max-w-[calc(100vw-2rem)] rounded-2xl border border-slate-600/80 bg-slate-800/98 shadow-2xl overflow-hidden">
+              <div className="p-4 space-y-3 text-sm">
+                <h3 className="font-semibold text-white">
+                  Lagrangian trajectory viewer · UPC
+                </h3>
+                <p className="text-slate-400">
+                  This viewer shows a{" "}
+                  <strong className="text-slate-300">
+                    Lagrangian particle simulation
+                  </strong>{" "}
+                  of the NW Mediterranean: particles are released from the
+                  Catalan coast and advected by a synthetic current field for 72
+                  hours.
+                </p>
+                <p className="text-slate-400">
+                  The approach is consistent with{" "}
+                  <a
+                    href="https://oceanparcels.org/"
+                    target="_blank"
+                    rel="noopener noreferrer"
+                    className="text-teal-400 hover:underline"
+                  >
+                    Ocean Parcels
+                  </a>
+                  : passive drifters are integrated in time; particles that hit
+                  the coast are marked as beached.
+                </p>
+                <p className="text-xs text-slate-500">
+                  Universitat Politècnica de Catalunya (UPC)
+                </p>
+              </div>
+            </div>
+          )}
+        </div>
+        <div className="relative">
+          <Button
+            variant="ghost"
+            size="sm"
+            className={`gap-2 rounded-lg px-4 py-2.5 text-sm font-medium transition-all ${
+              filtersOpen
+                ? "bg-teal-500/15 text-teal-300 border border-teal-500/40 shadow-sm"
+                : `border hover:border-slate-500 ${theme.text} ${theme.card} hover:opacity-90`
+            }`}
+            onClick={(e) => {
+              e.stopPropagation();
+              setFiltersOpen(!filtersOpen);
+            }}
+          >
+            <Filter className="size-4" />
+            Filters
+            <ChevronDown
+              className={`size-4 transition-transform ${filtersOpen ? "rotate-180" : ""}`}
+            />
+          </Button>
+          {filtersOpen && (
+            <div className="absolute right-0 top-full z-50 mt-2 w-80 rounded-2xl border border-slate-600/80 bg-slate-800/98 shadow-2xl overflow-hidden">
+              <div className="bg-slate-700/50 px-4 py-3 border-b border-slate-600/80">
+                <span className="flex items-center gap-2 text-sm font-semibold text-slate-200">
+                  <Layers className="size-4 text-teal-400" />
+                  Layers &amp; basemap
+                </span>
+                <p className="text-[11px] text-slate-500 mt-1">
+                  Basemap i capes
+                </p>
+              </div>
+              <div className="max-h-[70vh] overflow-y-auto p-4 space-y-5">
+                <div className="space-y-3">
+                  <p className="text-xs font-medium uppercase tracking-wider text-slate-400">
+                    Basemap
+                  </p>
+                  <div className="grid grid-cols-2 gap-2.5">
+                    {BASEMAPS.map((b) => {
+                      const isImage =
+                        b.thumb.startsWith("/") || b.thumb.startsWith("http");
+                      const selected = basemapId === b.id;
+                      return (
+                        <button
+                          key={b.id}
+                          type="button"
+                          onClick={() => setBasemapId(b.id)}
+                          className={`flex flex-col overflow-hidden rounded-xl border-2 text-left transition-all ${
+                            selected
+                              ? "border-teal-400 ring-2 ring-teal-400/30 shadow-lg shadow-teal-500/10"
+                              : "border-slate-600 hover:border-slate-500 bg-slate-700/40"
+                          }`}
+                        >
+                          <div className="relative h-14 w-full shrink-0 overflow-hidden bg-slate-700">
+                            {isImage ? (
+                              <img
+                                src={b.thumb}
+                                alt={b.name}
+                                className="h-full w-full object-cover"
+                                onError={(e) => {
+                                  e.currentTarget.style.display = "none";
+                                }}
+                              />
+                            ) : (
+                              <div
+                                className="h-full w-full"
+                                style={{ background: b.thumb }}
+                              />
+                            )}
+                            <div className="absolute inset-0 flex items-center justify-center opacity-40">
+                              <MapIcon className="size-6 text-slate-400" />
+                            </div>
+                            {selected && (
+                              <div className="absolute inset-0 bg-teal-500/10 pointer-events-none" />
+                            )}
+                          </div>
+                          <span
+                            className={`px-2.5 py-1.5 text-xs font-medium ${selected ? "text-teal-300" : "text-slate-300"}`}
+                          >
+                            {b.name}
+                          </span>
+                        </button>
+                      );
+                    })}
+                  </div>
+                </div>
+                <div className="space-y-3 pt-1 border-t border-slate-600/80">
+                  <p className="text-xs font-medium uppercase tracking-wider text-slate-400">
+                    Overlays
+                  </p>
+                  <div className="space-y-3 rounded-xl bg-slate-700/30 p-3">
+                    <div className="flex items-center justify-between gap-3">
+                      <div>
+                        <Label
+                          htmlFor="layer-trails"
+                          className="text-sm text-slate-200 cursor-pointer"
+                        >
+                          Trajectories
+                        </Label>
+                        <p className="text-[11px] text-slate-500">
+                          Particle paths over time
+                        </p>
+                      </div>
+                      <Switch
+                        id="layer-trails"
+                        checked={showTrails}
+                        onCheckedChange={setShowTrails}
+                      />
+                    </div>
+                    <div className="flex items-center justify-between gap-3">
+                      <div className="flex items-center gap-2 min-w-0">
+                        <span className="size-2 rounded-full bg-teal-400 shrink-0" />
+                        <div>
+                          <Label
+                            htmlFor="layer-active"
+                            className="text-sm text-slate-200 cursor-pointer"
+                          >
+                            Active particles
+                          </Label>
+                          <p className="text-[11px] text-slate-500">
+                            In water
+                          </p>
+                        </div>
+                      </div>
+                      <Switch
+                        id="layer-active"
+                        checked={showActiveParticles}
+                        onCheckedChange={setShowActiveParticles}
+                      />
+                    </div>
+                    <div className="flex items-center justify-between gap-3">
+                      <div className="flex items-center gap-2 min-w-0">
+                        <span className="size-2 rounded-full bg-red-500 shrink-0" />
+                        <div>
+                          <Label
+                            htmlFor="layer-beached"
+                            className="text-sm text-slate-200 cursor-pointer"
+                          >
+                            Beached particles
+                          </Label>
+                          <p className="text-[11px] text-slate-500">
+                            On coast
+                          </p>
+                        </div>
+                      </div>
+                      <Switch
+                        id="layer-beached"
+                        checked={showBeachedParticles}
+                        onCheckedChange={setShowBeachedParticles}
+                      />
+                    </div>
+                  </div>
+                </div>
+              </div>
+            </div>
+          )}
+        </div>
+      </div>
+    </header>
+  );
+}
--- a/frontend/src/components/MapView.tsx
+++ b/frontend/src/components/MapView.tsx
@ -0,0 +1,106 @@
+"use client";
+
+import { useCallback } from "react";
+import Map from "react-map-gl/maplibre";
+import { DeckGL } from "@deck.gl/react";
+import { ZoomIn, ZoomOut, Crosshair } from "lucide-react";
+import { Button } from "@/components/ui/button";
+import type { PointDatum } from "@/types/trajectory";
+
+export type ViewState = {
+  longitude: number;
+  latitude: number;
+  zoom: number;
+  pitch?: number;
+  bearing?: number;
+};
+
+interface MapViewProps {
+  viewState: ViewState;
+  setViewState: React.Dispatch<React.SetStateAction<ViewState>>;
+  layers: React.ComponentProps<typeof DeckGL>["layers"];
+  onClick: (opts: { object?: PointDatum }) => void;
+  getTooltip: (opts: { object?: PointDatum }) => { text: string } | null;
+  mapStyle: string;
+  /** When provided, shows a button to fit the map view to all particles. */
+  onFitToParticles?: () => void;
+}
+
+export function MapView({
+  viewState,
+  setViewState,
+  layers,
+  onClick,
+  getTooltip,
+  mapStyle,
+  onFitToParticles,
+}: MapViewProps) {
+  const zoomIn = useCallback(() => {
+    setViewState((v) => ({
+      ...v,
+      zoom: Math.min(18, (v.zoom ?? 7.5) + 1),
+    }));
+  }, [setViewState]);
+
+  const zoomOut = useCallback(() => {
+    setViewState((v) => ({
+      ...v,
+      zoom: Math.max(2, (v.zoom ?? 7.5) - 1),
+    }));
+  }, [setViewState]);
+
+  return (
+    <>
+      <DeckGL
+        viewState={viewState}
+        onViewStateChange={({ viewState: vs }) =>
+          setViewState((prev) => ({ ...prev, ...vs }))
+        }
+        controller
+        layers={layers}
+        onClick={({ object }) => onClick({ object: object as PointDatum })}
+        getTooltip={({ object }) =>
+          getTooltip({ object: object as PointDatum })
+        }
+      >
+        <Map mapStyle={mapStyle} />
+      </DeckGL>
+      <div className="absolute right-4 top-1/2 z-10 -translate-y-1/2 flex flex-col gap-1 rounded-xl border border-slate-600/80 bg-slate-800/95 shadow-xl backdrop-blur-sm p-1">
+        {onFitToParticles && (
+          <>
+            <Button
+              variant="outline"
+              size="icon"
+              className="h-11 w-11 rounded-lg border-slate-600 bg-slate-700/80 text-slate-200 hover:bg-slate-600 hover:text-white focus:ring-2 focus:ring-teal-500/50"
+              onClick={onFitToParticles}
+              title="Zoom a les partícules"
+              aria-label="Zoom a les partícules"
+            >
+              <Crosshair className="size-5" />
+            </Button>
+            <div className="h-px bg-slate-600/80 mx-1" />
+          </>
+        )}
+        <Button
+          variant="outline"
+          size="icon"
+          className="h-11 w-11 rounded-lg border-slate-600 bg-slate-700/80 text-slate-200 hover:bg-slate-600 hover:text-white focus:ring-2 focus:ring-teal-500/50"
+          onClick={zoomIn}
+          aria-label="Zoom in"
+        >
+          <ZoomIn className="size-5" />
+        </Button>
+        <div className="h-px bg-slate-600/80 mx-1" />
+        <Button
+          variant="outline"
+          size="icon"
+          className="h-11 w-11 rounded-lg border-slate-600 bg-slate-700/80 text-slate-200 hover:bg-slate-600 hover:text-white focus:ring-2 focus:ring-teal-500/50"
+          onClick={zoomOut}
+          aria-label="Zoom out"
+        >
+          <ZoomOut className="size-5" />
+        </Button>
+      </div>
+    </>
+  );
+}
--- a/frontend/src/components/TimePlayer.tsx
+++ b/frontend/src/components/TimePlayer.tsx
@ -0,0 +1,143 @@
+"use client";
+
+import { Play, Pause, ChevronLeft, ChevronRight, RotateCcw } from "lucide-react";
+import { Button } from "@/components/ui/button";
+import { Slider } from "@/components/ui/slider";
+import { SPEEDS } from "@/lib/constants";
+
+interface TimePlayerProps {
+  step: number;
+  onSlider: (value: number[]) => void;
+  maxStep: number;
+  day: number;
+  hour: number;
+  metaNumSteps: number;
+  metaNumParticles: number;
+  playing: boolean;
+  speedIdx: number;
+  togglePlay: () => void;
+  stepBack: () => void;
+  stepForward: () => void;
+  restart: () => void;
+  cycleSpeed: () => void;
+  /** When set, show calendar date instead of "Day X" (e.g. "27 Aug 06:00") */
+  dateLabel?: string | null;
+  startLabel?: string | null;
+  endLabel?: string | null;
+}
+
+export function TimePlayer({
+  step,
+  onSlider,
+  maxStep,
+  day,
+  hour,
+  metaNumSteps,
+  metaNumParticles,
+  playing,
+  speedIdx,
+  togglePlay,
+  stepBack,
+  stepForward,
+  restart,
+  cycleSpeed,
+  dateLabel = null,
+  startLabel = null,
+  endLabel = null,
+}: TimePlayerProps) {
+  const timeDisplay = dateLabel ?? `Day ${day} · ${hour.toString().padStart(2, "0")}:00`;
+  const sliderStart = startLabel ?? "Day 1 · 00:00";
+  const sliderEnd = endLabel ?? `Day ${Math.floor(maxStep / 24) + 1} · ${(maxStep % 24).toString().padStart(2, "0")}:00`;
+
+  return (
+    <div className="absolute bottom-4 left-1/2 z-10 w-full max-w-2xl -translate-x-1/2 rounded-xl border border-slate-600/80 bg-slate-800/95 shadow-xl backdrop-blur-md overflow-hidden">
+      <div className="px-3 py-2.5 space-y-2.5">
+        <div className="flex items-center gap-2 flex-wrap">
+          <div className="flex items-center gap-1">
+            <Button
+              size="icon"
+              variant="outline"
+              className="h-8 w-8 shrink-0 rounded-lg border-slate-600 bg-slate-700/80 text-slate-200 hover:bg-slate-600 hover:text-white"
+              onClick={stepBack}
+              disabled={step <= 0}
+              title="Anterior (←)"
+              aria-label="Step backward"
+            >
+              <ChevronLeft className="size-4" />
+            </Button>
+            <Button
+              size="icon"
+              className="h-10 w-10 shrink-0 rounded-xl bg-teal-500 hover:bg-teal-400 text-slate-900 shadow-md shadow-teal-500/30 focus:ring-2 focus:ring-teal-400 focus:ring-offset-2 focus:ring-offset-slate-800"
+              onClick={togglePlay}
+              title={playing ? "Pausar (Espai)" : "Reproduir (Espai)"}
+              aria-label={playing ? "Pause simulation" : "Play simulation"}
+            >
+              {playing ? (
+                <Pause className="size-5" />
+              ) : (
+                <Play className="size-5 ml-0.5" />
+              )}
+            </Button>
+            <Button
+              size="icon"
+              variant="outline"
+              className="h-8 w-8 shrink-0 rounded-lg border-slate-600 bg-slate-700/80 text-slate-200 hover:bg-slate-600 hover:text-white"
+              onClick={stepForward}
+              disabled={step >= maxStep}
+              title="Següent (→)"
+              aria-label="Step forward"
+            >
+              <ChevronRight className="size-4" />
+            </Button>
+          </div>
+          <div className="flex flex-col min-w-0">
+            <span className="text-lg font-bold tabular-nums text-white leading-tight">
+              {timeDisplay}
+            </span>
+            <span className="text-[11px] text-slate-400 leading-tight tabular-nums">
+              Step {step + 1} / {metaNumSteps}
+            </span>
+          </div>
+          <div className="flex items-center gap-1.5 ml-auto shrink-0">
+            <Button
+              variant="outline"
+              size="sm"
+              className="h-8 px-2.5 rounded-lg text-xs font-semibold border-slate-600 bg-slate-700/80 text-slate-200 hover:bg-slate-600 hover:text-white"
+              onClick={restart}
+              title="Reiniciar"
+              aria-label="Restart from beginning"
+            >
+              <RotateCcw className="size-3.5 mr-1" />
+              Restart
+            </Button>
+            <Button
+              variant="outline"
+              size="sm"
+              className="h-8 px-3 rounded-lg text-xs font-semibold border-slate-600 bg-slate-700/80 text-slate-200 hover:bg-slate-600 hover:text-white"
+              onClick={cycleSpeed}
+              title="Velocitat"
+              aria-label={`Playback speed: ${SPEEDS[speedIdx]}x`}
+            >
+              ×{SPEEDS[speedIdx]}
+            </Button>
+          </div>
+        </div>
+        <div className="space-y-1">
+          <Slider
+            min={0}
+            max={maxStep}
+            step={1}
+            value={[step]}
+            onValueChange={onSlider}
+            className="w-full py-2"
+            aria-label="Simulation time"
+          />
+          <div className="flex justify-between text-[11px] text-slate-400 px-0.5">
+            <span>{sliderStart}</span>
+            <span>{sliderEnd}</span>
+          </div>
+        </div>
+      </div>
+    </div>
+  );
+}
--- a/frontend/src/components/TrajectoryMap.tsx
+++ b/frontend/src/components/TrajectoryMap.tsx
@ -0,0 +1,375 @@
+"use client";
+
+import dynamic from "next/dynamic";
+import { useSearchParams } from "next/navigation";
+import { useCallback, useEffect, useMemo, useRef, useState } from "react";
+import "maplibre-gl/dist/maplibre-gl.css";
+
+import {
+  INIT_VIEW,
+  BASEMAPS,
+  TRAIL_LENGTH_HOURS,
+  TRAIL_STEP_STRIDE,
+} from "@/lib/constants";
+import { fitBounds } from "@math.gl/web-mercator";
+import {
+  buildScatterData,
+  buildTrails,
+  buildTripsWithTime,
+} from "@/lib/trajectoryData";
+import type { Meta, PointDatum } from "@/types/trajectory";
+import { useMetadata } from "@/hooks/useMetadata";
+import { useBlocks } from "@/hooks/useBlocks";
+import { useSimulation } from "@/hooks/useSimulation";
+import { useMapLayers } from "@/hooks/useMapLayers";
+import { IntroDialog, shouldShowIntro } from "@/components/IntroDialog";
+import { LoadingCard } from "@/components/LoadingCard";
+import { MapHeader } from "@/components/MapHeader";
+import { TimePlayer } from "@/components/TimePlayer";
+import type { ViewState } from "@/components/MapView";
+
+const MapView = dynamic(
+  () => import("@/components/MapView").then((m) => ({ default: m.MapView })),
+  { ssr: false, loading: () => <div className="flex h-full w-full items-center justify-center bg-background text-muted-foreground">Loading map…</div> }
+);
+
+const BLOCK_SIZE = 24;
+
+export default function TrajectoryMap() {
+  const [mounted, setMounted] = useState(false);
+  const [canvasReady, setCanvasReady] = useState(false);
+  const [showIntro, setShowIntro] = useState(true);
+  const [viewState, setViewState] = useState<ViewState>(INIT_VIEW);
+  const [basemapId, setBasemapId] = useState<
+    (typeof BASEMAPS)[number]["id"]
+  >("dark");
+  const [showTrails, setShowTrails] = useState(true);
+  const [showActiveParticles, setShowActiveParticles] = useState(true);
+  const [showBeachedParticles, setShowBeachedParticles] = useState(true);
+  const [filtersOpen, setFiltersOpen] = useState(false);
+  const [infoOpen, setInfoOpen] = useState(false);
+  const [selectedParticleId, setSelectedParticleId] = useState<number | null>(
+    null
+  );
+  const [accumulatedBeached, setAccumulatedBeached] = useState<
+    Map<number, [number, number]>
+  >(new Map());
+  const prevSimIdRef = useRef<string | null>(null);
+  const mapContainerRef = useRef<HTMLDivElement>(null);
+
+  const searchParams = useSearchParams();
+  const simId = searchParams.get("sim") ?? "default";
+  const meta = useMetadata(simId);
+  const { blocks, loadProgress, ready } = useBlocks(meta, simId);
+  const {
+    step,
+    setStep,
+    playing,
+    speedIdx,
+    togglePlay,
+    stepBack,
+    stepForward,
+    restart,
+    cycleSpeed,
+    onSlider,
+    maxStep,
+    day,
+    hour,
+    dateLabel,
+    startLabel,
+    endLabel,
+  } = useSimulation(meta);
+
+  useEffect(() => setMounted(true), []);
+
+  useEffect(() => {
+    setShowIntro((prev) => (prev ? shouldShowIntro() : false));
+  }, []);
+
+  // Defer DeckGL mount until after first paint so WebGL context is ready (avoids device.limits undefined in some browsers).
+  useEffect(() => {
+    if (!mounted) return;
+    let timeoutId: ReturnType<typeof setTimeout> | undefined;
+    let rafId2: number | null = null;
+    const rafId = requestAnimationFrame(() => {
+      rafId2 = requestAnimationFrame(() => {
+        timeoutId = setTimeout(() => setCanvasReady(true), 150);
+      });
+    });
+    return () => {
+      cancelAnimationFrame(rafId);
+      if (rafId2 != null) cancelAnimationFrame(rafId2);
+      if (timeoutId != null) clearTimeout(timeoutId);
+    };
+  }, [mounted]);
+
+  const blockIdx = Math.floor(step / BLOCK_SIZE);
+  const currentBlock = blocks[blockIdx];
+  const stepStart = currentBlock?.step_start ?? blockIdx * BLOCK_SIZE;
+  const frameIdx = step - stepStart;
+  const currentFrame =
+    currentBlock?.frames &&
+    frameIdx >= 0 &&
+    frameIdx < currentBlock.frames.length
+      ? currentBlock.frames[frameIdx]
+      : null;
+
+  // Reset accumulated beached when changing simulation
+  useEffect(() => {
+    if (prevSimIdRef.current !== null && prevSimIdRef.current !== simId) {
+      setAccumulatedBeached(new Map());
+    }
+    prevSimIdRef.current = simId;
+  }, [simId]);
+
+  // Accumulate beached particles from each frame so they don't disappear in later steps
+  useEffect(() => {
+    if (!currentFrame) return;
+    setAccumulatedBeached((prev) => {
+      const next = new Map(prev);
+      for (let i = 0; i < currentFrame.length; i++) {
+        if (currentFrame[i][4] === 1) {
+          next.set(i, [currentFrame[i][0], currentFrame[i][1]]);
+        }
+      }
+      return next;
+    });
+  }, [currentFrame]);
+
+  const scatterData = useMemo(
+    () => (currentFrame ? buildScatterData(currentFrame) : []),
+    [currentFrame]
+  );
+  const trailData = useMemo(
+    () =>
+      ready && meta
+        ? buildTrails(
+            blocks,
+            step,
+            meta.num_particles,
+            meta.release_steps,
+            TRAIL_STEP_STRIDE
+          )
+        : [],
+    [blocks, step, ready, meta]
+  );
+  const tripDataWithTime = useMemo(
+    () =>
+      ready && meta
+        ? buildTripsWithTime(
+            blocks,
+            step,
+            meta.num_particles,
+            meta.release_steps,
+            TRAIL_STEP_STRIDE
+          )
+        : [],
+    [blocks, step, ready, meta]
+  );
+
+  const currentTimeSec = step * 3600;
+  const trailLengthSec =
+    Math.min(meta?.num_steps ?? 72, TRAIL_LENGTH_HOURS) * 3600;
+
+  const accumulatedBeachedPts = useMemo(
+    () =>
+      Array.from(accumulatedBeached.entries()).map(([id, position]) => ({
+        id,
+        position,
+        beached: true as const,
+        speed: 0,
+      })),
+    [accumulatedBeached]
+  );
+  const beachedN = accumulatedBeached.size;
+  const activeN = (meta?.num_particles ?? 0) - beachedN;
+
+  /** Bounds [[minLon, minLat], [maxLon, maxLat]] for all current particles (frame + beached). */
+  const particleBounds = useMemo((): [[number, number], [number, number]] | null => {
+    const positions: [number, number][] = [
+      ...scatterData.map((d) => d.position),
+      ...accumulatedBeachedPts.map((d) => d.position),
+    ].filter(([lon, lat]) => Number.isFinite(lon) && Number.isFinite(lat));
+    if (positions.length === 0) return null;
+    let minLon = Infinity, maxLon = -Infinity, minLat = Infinity, maxLat = -Infinity;
+    for (const [lon, lat] of positions) {
+      minLon = Math.min(minLon, lon); maxLon = Math.max(maxLon, lon);
+      minLat = Math.min(minLat, lat); maxLat = Math.max(maxLat, lat);
+    }
+    if (!Number.isFinite(minLon) || !Number.isFinite(maxLon) || !Number.isFinite(minLat) || !Number.isFinite(maxLat)) return null;
+    const pad = 0.02;
+    if (maxLon - minLon < pad) { minLon -= pad / 2; maxLon += pad / 2; }
+    if (maxLat - minLat < pad) { minLat -= pad / 2; maxLat += pad / 2; }
+    return [[minLon, minLat], [maxLon, maxLat]];
+  }, [scatterData, accumulatedBeachedPts]);
+
+  const fitToParticles = useCallback(() => {
+    if (!particleBounds || !mapContainerRef.current) return;
+    const el = mapContainerRef.current;
+    const { width, height } = el.getBoundingClientRect();
+    const padding = 40;
+    if (width <= padding * 2 || height <= padding * 2) return;
+    try {
+      const view = fitBounds({
+        width,
+        height,
+        bounds: particleBounds,
+        padding,
+        minExtent: 0.01,
+        maxZoom: 14,
+      });
+      if (
+        Number.isFinite(view.zoom) &&
+        Number.isFinite(view.longitude) &&
+        Number.isFinite(view.latitude)
+      ) {
+        setViewState((prev) => ({ ...prev, ...view }));
+      }
+    } catch {
+      const [[minLon, minLat], [maxLon, maxLat]] = particleBounds;
+      const lon = (minLon + maxLon) / 2;
+      const lat = (minLat + maxLat) / 2;
+      if (Number.isFinite(lon) && Number.isFinite(lat)) {
+        setViewState((prev) => ({
+          ...prev,
+          longitude: lon,
+          latitude: lat,
+          zoom: Math.min(prev.zoom ?? 10, 12),
+        }));
+      }
+    }
+  }, [particleBounds]);
+
+  const layers = useMapLayers(
+    currentFrame,
+    scatterData,
+    trailData,
+    tripDataWithTime,
+    currentTimeSec,
+    trailLengthSec,
+    meta,
+    step,
+    selectedParticleId,
+    showTrails,
+    showActiveParticles,
+    showBeachedParticles,
+    accumulatedBeachedPts
+  );
+
+  const currentBasemap = useMemo(
+    () => BASEMAPS.find((b) => b.id === basemapId) ?? BASEMAPS[0],
+    [basemapId]
+  );
+
+  const safeViewState = useMemo(() => {
+    const { longitude, latitude, zoom } = viewState;
+    if (
+      Number.isFinite(longitude) &&
+      Number.isFinite(latitude) &&
+      Number.isFinite(zoom)
+    ) {
+      return viewState;
+    }
+    return {
+      ...viewState,
+      longitude: Number.isFinite(longitude) ? longitude : INIT_VIEW.longitude,
+      latitude: Number.isFinite(latitude) ? latitude : INIT_VIEW.latitude,
+      zoom: Number.isFinite(zoom) ? zoom : INIT_VIEW.zoom,
+    };
+  }, [viewState]);
+
+  const onMapClick = useCallback(({ object }: { object?: PointDatum }) => {
+    if (object && typeof object.id === "number") {
+      setSelectedParticleId((prev) =>
+        prev === object.id ? null : object.id
+      );
+    } else {
+      setSelectedParticleId(null);
+    }
+  }, []);
+
+  const getTooltip = useCallback(
+    ({ object }: { object?: PointDatum }) => {
+      if (!object || !meta) return null;
+      const origin = meta.seed_names[meta.origins[object.id]] ?? "?";
+      return {
+        text: object.beached
+          ? `#${object.id} · Beached · Origin: ${origin} (click to select)`
+          : `#${object.id} · ${object.speed.toFixed(3)} m/s · Origin: ${origin} (click to select)`,
+      };
+    },
+    [meta]
+  );
+
+  return (
+    <>
+      <IntroDialog open={showIntro} onOpenChange={setShowIntro} />
+
+      {!ready && (
+        <LoadingCard meta={meta} loadProgress={loadProgress} />
+      )}
+
+      {ready && (
+        <div className="relative h-full w-full">
+          {!mounted || !canvasReady ? (
+            <div className="flex h-full w-full items-center justify-center bg-background text-muted-foreground">
+              Preparing map…
+            </div>
+          ) : (
+            <div ref={mapContainerRef} className="absolute inset-0">
+              <MapView
+                viewState={safeViewState}
+                setViewState={setViewState}
+                layers={layers}
+                onClick={onMapClick}
+                getTooltip={getTooltip}
+                mapStyle={currentBasemap.url}
+                onFitToParticles={particleBounds ? fitToParticles : undefined}
+              />
+
+              <MapHeader
+                basemapId={basemapId}
+                setBasemapId={setBasemapId}
+                day={day}
+                hour={hour}
+                dateLabel={dateLabel}
+                activeN={activeN}
+                beachedN={beachedN}
+                filtersOpen={filtersOpen}
+                setFiltersOpen={setFiltersOpen}
+                infoOpen={infoOpen}
+                setInfoOpen={setInfoOpen}
+                showTrails={showTrails}
+                setShowTrails={setShowTrails}
+                showActiveParticles={showActiveParticles}
+                setShowActiveParticles={setShowActiveParticles}
+                showBeachedParticles={showBeachedParticles}
+                setShowBeachedParticles={setShowBeachedParticles}
+              />
+
+              <TimePlayer
+                step={step}
+                onSlider={onSlider}
+                maxStep={maxStep}
+                day={day}
+                hour={hour}
+                metaNumSteps={meta?.num_steps ?? 0}
+                metaNumParticles={meta?.num_particles ?? 0}
+                playing={playing}
+                speedIdx={speedIdx}
+                togglePlay={togglePlay}
+                stepBack={stepBack}
+                stepForward={stepForward}
+                restart={restart}
+                cycleSpeed={cycleSpeed}
+                dateLabel={dateLabel}
+                startLabel={startLabel}
+                endLabel={endLabel}
+              />
+            </div>
+          )}
+        </div>
+      )}
+    </>
+  );
+}
--- a/frontend/src/components/ui/button.tsx
+++ b/frontend/src/components/ui/button.tsx
@ -0,0 +1,64 @@
+import * as React from "react"
+import { cva, type VariantProps } from "class-variance-authority"
+import { Slot } from "radix-ui"
+
+import { cn } from "@/lib/utils"
+
+const buttonVariants = cva(
+  "inline-flex items-center justify-center gap-2 whitespace-nowrap rounded-md text-sm font-medium transition-all disabled:pointer-events-none disabled:opacity-50 [&_svg]:pointer-events-none [&_svg:not([class*='size-'])]:size-4 shrink-0 [&_svg]:shrink-0 outline-none focus-visible:border-ring focus-visible:ring-ring/50 focus-visible:ring-[3px] aria-invalid:ring-destructive/20 dark:aria-invalid:ring-destructive/40 aria-invalid:border-destructive",
+  {
+    variants: {
+      variant: {
+        default: "bg-primary text-primary-foreground hover:bg-primary/90",
+        destructive:
+          "bg-destructive text-white hover:bg-destructive/90 focus-visible:ring-destructive/20 dark:focus-visible:ring-destructive/40 dark:bg-destructive/60",
+        outline:
+          "border bg-background shadow-xs hover:bg-accent hover:text-accent-foreground dark:bg-input/30 dark:border-input dark:hover:bg-input/50",
+        secondary:
+          "bg-secondary text-secondary-foreground hover:bg-secondary/80",
+        ghost:
+          "hover:bg-accent hover:text-accent-foreground dark:hover:bg-accent/50",
+        link: "text-primary underline-offset-4 hover:underline",
+      },
+      size: {
+        default: "h-9 px-4 py-2 has-[>svg]:px-3",
+        xs: "h-6 gap-1 rounded-md px-2 text-xs has-[>svg]:px-1.5 [&_svg:not([class*='size-'])]:size-3",
+        sm: "h-8 rounded-md gap-1.5 px-3 has-[>svg]:px-2.5",
+        lg: "h-10 rounded-md px-6 has-[>svg]:px-4",
+        icon: "size-9",
+        "icon-xs": "size-6 rounded-md [&_svg:not([class*='size-'])]:size-3",
+        "icon-sm": "size-8",
+        "icon-lg": "size-10",
+      },
+    },
+    defaultVariants: {
+      variant: "default",
+      size: "default",
+    },
+  }
+)
+
+function Button({
+  className,
+  variant = "default",
+  size = "default",
+  asChild = false,
+  ...props
+}: React.ComponentProps<"button"> &
+  VariantProps<typeof buttonVariants> & {
+    asChild?: boolean
+  }) {
+  const Comp = asChild ? Slot.Root : "button"
+
+  return (
+    <Comp
+      data-slot="button"
+      data-variant={variant}
+      data-size={size}
+      className={cn(buttonVariants({ variant, size, className }))}
+      {...props}
+    />
+  )
+}
+
+export { Button, buttonVariants }
--- a/frontend/src/components/ui/card.tsx
+++ b/frontend/src/components/ui/card.tsx
@ -0,0 +1,92 @@
+import * as React from "react"
+
+import { cn } from "@/lib/utils"
+
+function Card({ className, ...props }: React.ComponentProps<"div">) {
+  return (
+    <div
+      data-slot="card"
+      className={cn(
+        "bg-card text-card-foreground flex flex-col gap-6 rounded-xl border py-6 shadow-sm",
+        className
+      )}
+      {...props}
+    />
+  )
+}
+
+function CardHeader({ className, ...props }: React.ComponentProps<"div">) {
+  return (
+    <div
+      data-slot="card-header"
+      className={cn(
+        "@container/card-header grid auto-rows-min grid-rows-[auto_auto] items-start gap-2 px-6 has-data-[slot=card-action]:grid-cols-[1fr_auto] [.border-b]:pb-6",
+        className
+      )}
+      {...props}
+    />
+  )
+}
+
+function CardTitle({ className, ...props }: React.ComponentProps<"div">) {
+  return (
+    <div
+      data-slot="card-title"
+      className={cn("leading-none font-semibold", className)}
+      {...props}
+    />
+  )
+}
+
+function CardDescription({ className, ...props }: React.ComponentProps<"div">) {
+  return (
+    <div
+      data-slot="card-description"
+      className={cn("text-muted-foreground text-sm", className)}
+      {...props}
+    />
+  )
+}
+
+function CardAction({ className, ...props }: React.ComponentProps<"div">) {
+  return (
+    <div
+      data-slot="card-action"
+      className={cn(
+        "col-start-2 row-span-2 row-start-1 self-start justify-self-end",
+        className
+      )}
+      {...props}
+    />
+  )
+}
+
+function CardContent({ className, ...props }: React.ComponentProps<"div">) {
+  return (
+    <div
+      data-slot="card-content"
+      className={cn("px-6", className)}
+      {...props}
+    />
+  )
+}
+
+function CardFooter({ className, ...props }: React.ComponentProps<"div">) {
+  return (
+    <div
+      data-slot="card-footer"
+      className={cn("flex items-center px-6 [.border-t]:pt-6", className)}
+      {...props}
+    />
+  )
+}
+
+export {
+  Card,
+  CardHeader,
+  CardFooter,
+  CardTitle,
+  CardAction,
+  CardDescription,
+  CardContent,
+}
--- a/frontend/src/components/ui/dialog.tsx
+++ b/frontend/src/components/ui/dialog.tsx
@ -0,0 +1,158 @@
+"use client"
+
+import * as React from "react"
+import { XIcon } from "lucide-react"
+import { Dialog as DialogPrimitive } from "radix-ui"
+
+import { cn } from "@/lib/utils"
+import { Button } from "@/components/ui/button"
+
+function Dialog({
+  ...props
+}: React.ComponentProps<typeof DialogPrimitive.Root>) {
+  return <DialogPrimitive.Root data-slot="dialog" {...props} />
+}
+
+function DialogTrigger({
+  ...props
+}: React.ComponentProps<typeof DialogPrimitive.Trigger>) {
+  return <DialogPrimitive.Trigger data-slot="dialog-trigger" {...props} />
+}
+
+function DialogPortal({
+  ...props
+}: React.ComponentProps<typeof DialogPrimitive.Portal>) {
+  return <DialogPrimitive.Portal data-slot="dialog-portal" {...props} />
+}
+
+function DialogClose({
+  ...props
+}: React.ComponentProps<typeof DialogPrimitive.Close>) {
+  return <DialogPrimitive.Close data-slot="dialog-close" {...props} />
+}
+
+function DialogOverlay({
+  className,
+  ...props
+}: React.ComponentProps<typeof DialogPrimitive.Overlay>) {
+  return (
+    <DialogPrimitive.Overlay
+      data-slot="dialog-overlay"
+      className={cn(
+        "data-[state=open]:animate-in data-[state=closed]:animate-out data-[state=closed]:fade-out-0 data-[state=open]:fade-in-0 fixed inset-0 z-50 bg-black/50",
+        className
+      )}
+      {...props}
+    />
+  )
+}
+
+function DialogContent({
+  className,
+  children,
+  showCloseButton = true,
+  ...props
+}: React.ComponentProps<typeof DialogPrimitive.Content> & {
+  showCloseButton?: boolean
+}) {
+  return (
+    <DialogPortal data-slot="dialog-portal">
+      <DialogOverlay />
+      <DialogPrimitive.Content
+        data-slot="dialog-content"
+        className={cn(
+          "bg-background data-[state=open]:animate-in data-[state=closed]:animate-out data-[state=closed]:fade-out-0 data-[state=open]:fade-in-0 data-[state=closed]:zoom-out-95 data-[state=open]:zoom-in-95 fixed top-[50%] left-[50%] z-50 grid w-full max-w-[calc(100%-2rem)] translate-x-[-50%] translate-y-[-50%] gap-4 rounded-lg border p-6 shadow-lg duration-200 outline-none sm:max-w-lg",
+          className
+        )}
+        {...props}
+      >
+        {children}
+        {showCloseButton && (
+          <DialogPrimitive.Close
+            data-slot="dialog-close"
+            className="ring-offset-background focus:ring-ring data-[state=open]:bg-accent data-[state=open]:text-muted-foreground absolute top-4 right-4 rounded-xs opacity-70 transition-opacity hover:opacity-100 focus:ring-2 focus:ring-offset-2 focus:outline-hidden disabled:pointer-events-none [&_svg]:pointer-events-none [&_svg]:shrink-0 [&_svg:not([class*='size-'])]:size-4"
+          >
+            <XIcon />
+            <span className="sr-only">Close</span>
+          </DialogPrimitive.Close>
+        )}
+      </DialogPrimitive.Content>
+    </DialogPortal>
+  )
+}
+
+function DialogHeader({ className, ...props }: React.ComponentProps<"div">) {
+  return (
+    <div
+      data-slot="dialog-header"
+      className={cn("flex flex-col gap-2 text-center sm:text-left", className)}
+      {...props}
+    />
+  )
+}
+
+function DialogFooter({
+  className,
+  showCloseButton = false,
+  children,
+  ...props
+}: React.ComponentProps<"div"> & {
+  showCloseButton?: boolean
+}) {
+  return (
+    <div
+      data-slot="dialog-footer"
+      className={cn(
+        "flex flex-col-reverse gap-2 sm:flex-row sm:justify-end",
+        className
+      )}
+      {...props}
+    >
+      {children}
+      {showCloseButton && (
+        <DialogPrimitive.Close asChild>
+          <Button variant="outline">Close</Button>
+        </DialogPrimitive.Close>
+      )}
+    </div>
+  )
+}
+
+function DialogTitle({
+  className,
+  ...props
+}: React.ComponentProps<typeof DialogPrimitive.Title>) {
+  return (
+    <DialogPrimitive.Title
+      data-slot="dialog-title"
+      className={cn("text-lg leading-none font-semibold", className)}
+      {...props}
+    />
+  )
+}
+
+function DialogDescription({
+  className,
+  ...props
+}: React.ComponentProps<typeof DialogPrimitive.Description>) {
+  return (
+    <DialogPrimitive.Description
+      data-slot="dialog-description"
+      className={cn("text-muted-foreground text-sm", className)}
+      {...props}
+    />
+  )
+}
+
+export {
+  Dialog,
+  DialogClose,
+  DialogContent,
+  DialogDescription,
+  DialogFooter,
+  DialogHeader,
+  DialogOverlay,
+  DialogPortal,
+  DialogTitle,
+  DialogTrigger,
+}
--- a/frontend/src/components/ui/label.tsx
+++ b/frontend/src/components/ui/label.tsx
@ -0,0 +1,24 @@
+"use client"
+
+import * as React from "react"
+import { Label as LabelPrimitive } from "radix-ui"
+
+import { cn } from "@/lib/utils"
+
+function Label({
+  className,
+  ...props
+}: React.ComponentProps<typeof LabelPrimitive.Root>) {
+  return (
+    <LabelPrimitive.Root
+      data-slot="label"
+      className={cn(
+        "flex items-center gap-2 text-sm leading-none font-medium select-none group-data-[disabled=true]:pointer-events-none group-data-[disabled=true]:opacity-50 peer-disabled:cursor-not-allowed peer-disabled:opacity-50",
+        className
+      )}
+      {...props}
+    />
+  )
+}
+
+export { Label }
--- a/frontend/src/components/ui/progress.tsx
+++ b/frontend/src/components/ui/progress.tsx
@ -0,0 +1,31 @@
+"use client"
+
+import * as React from "react"
+import { Progress as ProgressPrimitive } from "radix-ui"
+
+import { cn } from "@/lib/utils"
+
+function Progress({
+  className,
+  value,
+  ...props
+}: React.ComponentProps<typeof ProgressPrimitive.Root>) {
+  return (
+    <ProgressPrimitive.Root
+      data-slot="progress"
+      className={cn(
+        "bg-primary/20 relative h-2 w-full overflow-hidden rounded-full",
+        className
+      )}
+      {...props}
+    >
+      <ProgressPrimitive.Indicator
+        data-slot="progress-indicator"
+        className="bg-primary h-full w-full flex-1 transition-all"
+        style={{ transform: `translateX(-${100 - (value || 0)}%)` }}
+      />
+    </ProgressPrimitive.Root>
+  )
+}
+
+export { Progress }
--- a/frontend/src/components/ui/sheet.tsx
+++ b/frontend/src/components/ui/sheet.tsx
@ -0,0 +1,143 @@
+"use client"
+
+import * as React from "react"
+import { XIcon } from "lucide-react"
+import { Dialog as SheetPrimitive } from "radix-ui"
+
+import { cn } from "@/lib/utils"
+
+function Sheet({ ...props }: React.ComponentProps<typeof SheetPrimitive.Root>) {
+  return <SheetPrimitive.Root data-slot="sheet" {...props} />
+}
+
+function SheetTrigger({
+  ...props
+}: React.ComponentProps<typeof SheetPrimitive.Trigger>) {
+  return <SheetPrimitive.Trigger data-slot="sheet-trigger" {...props} />
+}
+
+function SheetClose({
+  ...props
+}: React.ComponentProps<typeof SheetPrimitive.Close>) {
+  return <SheetPrimitive.Close data-slot="sheet-close" {...props} />
+}
+
+function SheetPortal({
+  ...props
+}: React.ComponentProps<typeof SheetPrimitive.Portal>) {
+  return <SheetPrimitive.Portal data-slot="sheet-portal" {...props} />
+}
+
+function SheetOverlay({
+  className,
+  ...props
+}: React.ComponentProps<typeof SheetPrimitive.Overlay>) {
+  return (
+    <SheetPrimitive.Overlay
+      data-slot="sheet-overlay"
+      className={cn(
+        "data-[state=open]:animate-in data-[state=closed]:animate-out data-[state=closed]:fade-out-0 data-[state=open]:fade-in-0 fixed inset-0 z-50 bg-black/50",
+        className
+      )}
+      {...props}
+    />
+  )
+}
+
+function SheetContent({
+  className,
+  children,
+  side = "right",
+  showCloseButton = true,
+  ...props
+}: React.ComponentProps<typeof SheetPrimitive.Content> & {
+  side?: "top" | "right" | "bottom" | "left"
+  showCloseButton?: boolean
+}) {
+  return (
+    <SheetPortal>
+      <SheetOverlay />
+      <SheetPrimitive.Content
+        data-slot="sheet-content"
+        className={cn(
+          "bg-background data-[state=open]:animate-in data-[state=closed]:animate-out fixed z-50 flex flex-col gap-4 shadow-lg transition ease-in-out data-[state=closed]:duration-300 data-[state=open]:duration-500",
+          side === "right" &&
+            "data-[state=closed]:slide-out-to-right data-[state=open]:slide-in-from-right inset-y-0 right-0 h-full w-3/4 border-l sm:max-w-sm",
+          side === "left" &&
+            "data-[state=closed]:slide-out-to-left data-[state=open]:slide-in-from-left inset-y-0 left-0 h-full w-3/4 border-r sm:max-w-sm",
+          side === "top" &&
+            "data-[state=closed]:slide-out-to-top data-[state=open]:slide-in-from-top inset-x-0 top-0 h-auto border-b",
+          side === "bottom" &&
+            "data-[state=closed]:slide-out-to-bottom data-[state=open]:slide-in-from-bottom inset-x-0 bottom-0 h-auto border-t",
+          className
+        )}
+        {...props}
+      >
+        {children}
+        {showCloseButton && (
+          <SheetPrimitive.Close className="ring-offset-background focus:ring-ring data-[state=open]:bg-secondary absolute top-4 right-4 rounded-xs opacity-70 transition-opacity hover:opacity-100 focus:ring-2 focus:ring-offset-2 focus:outline-hidden disabled:pointer-events-none">
+            <XIcon className="size-4" />
+            <span className="sr-only">Close</span>
+          </SheetPrimitive.Close>
+        )}
+      </SheetPrimitive.Content>
+    </SheetPortal>
+  )
+}
+
+function SheetHeader({ className, ...props }: React.ComponentProps<"div">) {
+  return (
+    <div
+      data-slot="sheet-header"
+      className={cn("flex flex-col gap-1.5 p-4", className)}
+      {...props}
+    />
+  )
+}
+
+function SheetFooter({ className, ...props }: React.ComponentProps<"div">) {
+  return (
+    <div
+      data-slot="sheet-footer"
+      className={cn("mt-auto flex flex-col gap-2 p-4", className)}
+      {...props}
+    />
+  )
+}
+
+function SheetTitle({
+  className,
+  ...props
+}: React.ComponentProps<typeof SheetPrimitive.Title>) {
+  return (
+    <SheetPrimitive.Title
+      data-slot="sheet-title"
+      className={cn("text-foreground font-semibold", className)}
+      {...props}
+    />
+  )
+}
+
+function SheetDescription({
+  className,
+  ...props
+}: React.ComponentProps<typeof SheetPrimitive.Description>) {
+  return (
+    <SheetPrimitive.Description
+      data-slot="sheet-description"
+      className={cn("text-muted-foreground text-sm", className)}
+      {...props}
+    />
+  )
+}
+
+export {
+  Sheet,
+  SheetTrigger,
+  SheetClose,
+  SheetContent,
+  SheetHeader,
+  SheetFooter,
+  SheetTitle,
+  SheetDescription,
+}
--- a/frontend/src/components/ui/slider.tsx
+++ b/frontend/src/components/ui/slider.tsx
@ -0,0 +1,63 @@
+"use client"
+
+import * as React from "react"
+import { Slider as SliderPrimitive } from "radix-ui"
+
+import { cn } from "@/lib/utils"
+
+function Slider({
+  className,
+  defaultValue,
+  value,
+  min = 0,
+  max = 100,
+  ...props
+}: React.ComponentProps<typeof SliderPrimitive.Root>) {
+  const _values = React.useMemo(
+    () =>
+      Array.isArray(value)
+        ? value
+        : Array.isArray(defaultValue)
+          ? defaultValue
+          : [min, max],
+    [value, defaultValue, min, max]
+  )
+
+  return (
+    <SliderPrimitive.Root
+      data-slot="slider"
+      defaultValue={defaultValue}
+      value={value}
+      min={min}
+      max={max}
+      className={cn(
+        "relative flex w-full touch-none items-center select-none data-[disabled]:opacity-50 data-[orientation=vertical]:h-full data-[orientation=vertical]:min-h-44 data-[orientation=vertical]:w-auto data-[orientation=vertical]:flex-col",
+        className
+      )}
+      {...props}
+    >
+      <SliderPrimitive.Track
+        data-slot="slider-track"
+        className={cn(
+          "bg-muted relative grow overflow-hidden rounded-full data-[orientation=horizontal]:h-1.5 data-[orientation=horizontal]:w-full data-[orientation=vertical]:h-full data-[orientation=vertical]:w-1.5"
+        )}
+      >
+        <SliderPrimitive.Range
+          data-slot="slider-range"
+          className={cn(
+            "bg-primary absolute data-[orientation=horizontal]:h-full data-[orientation=vertical]:w-full"
+          )}
+        />
+      </SliderPrimitive.Track>
+      {Array.from({ length: _values.length }, (_, index) => (
+        <SliderPrimitive.Thumb
+          data-slot="slider-thumb"
+          key={index}
+          className="border-primary ring-ring/50 block size-4 shrink-0 rounded-full border bg-white shadow-sm transition-[color,box-shadow] hover:ring-4 focus-visible:ring-4 focus-visible:outline-hidden disabled:pointer-events-none disabled:opacity-50"
+        />
+      ))}
+    </SliderPrimitive.Root>
+  )
+}
+
+export { Slider }
--- a/frontend/src/components/ui/switch.tsx
+++ b/frontend/src/components/ui/switch.tsx
@ -0,0 +1,35 @@
+"use client"
+
+import * as React from "react"
+import { Switch as SwitchPrimitive } from "radix-ui"
+
+import { cn } from "@/lib/utils"
+
+function Switch({
+  className,
+  size = "default",
+  ...props
+}: React.ComponentProps<typeof SwitchPrimitive.Root> & {
+  size?: "sm" | "default"
+}) {
+  return (
+    <SwitchPrimitive.Root
+      data-slot="switch"
+      data-size={size}
+      className={cn(
+        "peer data-[state=checked]:bg-primary data-[state=unchecked]:bg-input focus-visible:border-ring focus-visible:ring-ring/50 dark:data-[state=unchecked]:bg-input/80 group/switch inline-flex shrink-0 items-center rounded-full border border-transparent shadow-xs transition-all outline-none focus-visible:ring-[3px] disabled:cursor-not-allowed disabled:opacity-50 data-[size=default]:h-[1.15rem] data-[size=default]:w-8 data-[size=sm]:h-3.5 data-[size=sm]:w-6",
+        className
+      )}
+      {...props}
+    >
+      <SwitchPrimitive.Thumb
+        data-slot="switch-thumb"
+        className={cn(
+          "bg-background dark:data-[state=unchecked]:bg-foreground dark:data-[state=checked]:bg-primary-foreground pointer-events-none block rounded-full ring-0 transition-transform group-data-[size=default]/switch:size-4 group-data-[size=sm]/switch:size-3 data-[state=checked]:translate-x-[calc(100%-2px)] data-[state=unchecked]:translate-x-0"
+        )}
+      />
+    </SwitchPrimitive.Root>
+  )
+}
+
+export { Switch }
--- a/frontend/src/hooks/useBlocks.ts
+++ b/frontend/src/hooks/useBlocks.ts
@ -0,0 +1,80 @@
+import { useEffect, useState } from "react";
+import { tableFromIPC } from "apache-arrow";
+import { API, USE_ARROW } from "@/lib/constants";
+import type { Block, Meta } from "@/types/trajectory";
+import { framesFromArrowTable } from "@/lib/trajectoryData";
+
+export function useBlocks(
+  meta: Meta | null,
+  simId: string = "default"
+): {
+  blocks: (Block | null)[];
+  loadProgress: number;
+  ready: boolean;
+} {
+  const [blocks, setBlocks] = useState<(Block | null)[]>([null, null, null]);
+  const [loadProgress, setLoadProgress] = useState(0);
+  const [ready, setReady] = useState(false);
+
+  useEffect(() => {
+    if (!meta) return;
+    const nBlocks = meta.num_blocks;
+    const nParticles = meta.num_particles;
+    const simParam = `sim=${encodeURIComponent(simId)}`;
+    let loaded = 0;
+    const result: (Block | null)[] = new Array(nBlocks).fill(null);
+    setBlocks(result);
+    setReady(false);
+
+    function onBlockLoaded(i: number, block: Block | null) {
+      result[i] = block;
+      loaded++;
+      setLoadProgress(Math.round((loaded / nBlocks) * 100));
+      if (loaded === nBlocks) {
+        setBlocks([...result]);
+        setReady(true);
+      } else {
+        setBlocks((prev) => {
+          const next = Array.from({ length: nBlocks }, (_, j) => (j === i ? block : prev[j] ?? result[j] ?? null));
+          return next;
+        });
+      }
+    }
+
+    async function loadBlock(i: number) {
+      try {
+        if (USE_ARROW) {
+          const [metaRes, arrowRes] = await Promise.all([
+            fetch(`${API}/api/block/${i}?frames=false&${simParam}`),
+            fetch(`${API}/api/block/${i}/arrow?${simParam}`),
+          ]);
+          if (metaRes.ok && arrowRes.ok) {
+            const metaBlock = (await metaRes.json()) as Pick<
+              Block,
+              "block" | "step_start" | "step_end" | "accumulation"
+            >;
+            const buf = await arrowRes.arrayBuffer();
+            const table = tableFromIPC(new Uint8Array(buf));
+            const frames = framesFromArrowTable(table, nParticles);
+            onBlockLoaded(i, { ...metaBlock, frames });
+            return;
+          }
+        }
+      } catch {
+        /* fallback to JSON */
+      }
+      try {
+        const full = (await fetch(`${API}/api/block/${i}?${simParam}`).then((r) =>
+          r.json()
+        )) as Block;
+        onBlockLoaded(i, full);
+      } catch {
+        onBlockLoaded(i, null);
+      }
+    }
+
+    for (let i = 0; i < nBlocks; i++) loadBlock(i);
+  }, [meta, simId]);
+
+  return { blocks, loadProgress, ready };
+}
--- a/frontend/src/hooks/useClickOutside.ts
+++ b/frontend/src/hooks/useClickOutside.ts
@ -0,0 +1,16 @@
+import { useEffect, type RefObject } from "react";
+
+export function useClickOutside<T extends HTMLElement>(
+  ref: RefObject<T | null>,
+  isOpen: boolean,
+  onClose: () => void
+): void {
+  useEffect(() => {
+    if (!isOpen) return;
+    const onDocClick = (e: MouseEvent) => {
+      if (ref.current && !ref.current.contains(e.target as Node)) onClose();
+    };
+    document.addEventListener("click", onDocClick);
+    return () => document.removeEventListener("click", onDocClick);
+  }, [isOpen, onClose, ref]);
+}
--- a/frontend/src/hooks/useMapLayers.ts
+++ b/frontend/src/hooks/useMapLayers.ts
@ -0,0 +1,258 @@
+import { useMemo } from "react";
+import { PathLayer, ScatterplotLayer } from "@deck.gl/layers";
+import { TripsLayer } from "@deck.gl/geo-layers";
+import type {
+  TrailDatum,
+  TripDatum,
+  PointDatum,
+  Meta,
+  Frame,
+} from "@/types/trajectory";
+import {
+  C_TRAIL_ACTIVE,
+  C_TRAIL_BEACHED,
+  C_GLOW_ACTIVE,
+  C_GLOW_BEACHED,
+  C_BLOOM_ACTIVE,
+  C_BLOOM_BEACHED,
+  C_SELECTED,
+  C_BEACHED,
+  PALETTE_ORIGIN,
+  activeColor,
+} from "@/lib/constants";
+
+type Layer =
+  | PathLayer<TrailDatum>
+  | TripsLayer<TripDatum>
+  | ScatterplotLayer<PointDatum>;
+
+type TripColor =
+  | [number, number, number, number]
+  | ((d: TripDatum) => [number, number, number, number]);
+
+/** Thin streamlines, caps arrodonits, smooth joints; color fix o per origen */
+function createTripsLayer(
+  id: string,
+  data: TripDatum[],
+  color: TripColor,
+  currentTimeSec: number,
+  trailLengthSec: number,
+  widthMinPixels: number,
+  widthMaxPixels: number
+): TripsLayer<TripDatum> {
+  return new TripsLayer<TripDatum>({
+    id,
+    data,
+    getPath: (d) => d.path.flatMap((p) => [p[0], p[1]]),
+    getTimestamps: (d) => d.path.map((p) => p[2]),
+    getColor: color,
+    currentTime: currentTimeSec,
+    trailLength: trailLengthSec,
+    fadeTrail: true,
+    widthMinPixels,
+    widthMaxPixels,
+    capRounded: true,
+    jointRounded: true,
+    positionFormat: "XY",
+  });
+}
+
+function getColorByOrigin(
+  meta: Meta | null,
+  alpha: number
+): (d: TripDatum) => [number, number, number, number] {
+  return (d) => {
+    const idx = meta?.origins?.[d.id] ?? 0;
+    const [r, g, b] = PALETTE_ORIGIN[idx % PALETTE_ORIGIN.length];
+    return [r, g, b, alpha];
+  };
+}
+
+export function useMapLayers(
+  currentFrame: Frame | null,
+  scatterData: PointDatum[],
+  trailData: TrailDatum[],
+  tripDataWithTime: TripDatum[],
+  currentTimeSec: number,
+  trailLengthSec: number,
+  meta: Meta | null,
+  step: number,
+  selectedParticleId: number | null,
+  showTrails: boolean,
+  showActiveParticles: boolean,
+  showBeachedParticles: boolean,
+  accumulatedBeachedPts: PointDatum[] = []
+): Layer[] {
+  const activePts = useMemo(() => {
+    if (!scatterData.length) return [];
+    return scatterData.filter((p) => {
+      if (meta?.release_steps && meta.release_steps[p.id] > step) return false;
+      return !p.beached;
+    });
+  }, [scatterData, meta, step]);
+
+  const beachedPtsFromScatter = useMemo(() => {
+    if (!scatterData.length) return [];
+    return scatterData.filter((p) => {
+      if (meta?.release_steps && meta.release_steps[p.id] > step)
+        return false;
+      return p.beached;
+    });
+  }, [scatterData, meta, step]);
+
+  const beachedPts =
+    accumulatedBeachedPts.length > 0 ? accumulatedBeachedPts : beachedPtsFromScatter;
+
+  return useMemo(() => {
+    if (!currentFrame) return [];
+    const out: Layer[] = [];
+
+    if (showTrails && tripDataWithTime.length > 0) {
+      const activeTrips = tripDataWithTime.filter((t) => !t.beached);
+      const beachedTrips = tripDataWithTime.filter((t) => t.beached);
+      if (activeTrips.length) {
+        const activeBloomColor = meta
+          ? getColorByOrigin(meta, 40)
+          : C_BLOOM_ACTIVE;
+        const activeGlowColor = meta
+          ? getColorByOrigin(meta, 120)
+          : C_GLOW_ACTIVE;
+        const activeCoreColor = meta
+          ? getColorByOrigin(meta, 255)
+          : C_TRAIL_ACTIVE;
+        out.push(
+          createTripsLayer(
+            "trips-active-bloom",
+            activeTrips,
+            activeBloomColor,
+            currentTimeSec,
+            trailLengthSec,
+            2,
+            8
+          )
+        );
+        out.push(
+          createTripsLayer(
+            "trips-active-glow",
+            activeTrips,
+            activeGlowColor,
+            currentTimeSec,
+            trailLengthSec,
+            1,
+            4
+          )
+        );
+        out.push(
+          createTripsLayer(
+            "trips-active",
+            activeTrips,
+            activeCoreColor,
+            currentTimeSec,
+            trailLengthSec,
+            0.8,
+            2.2
+          )
+        );
+      }
+      if (beachedTrips.length) {
+        out.push(
+          createTripsLayer(
+            "trips-beached-bloom",
+            beachedTrips,
+            C_BLOOM_BEACHED,
+            currentTimeSec,
+            trailLengthSec,
+            1.5,
+            5
+          )
+        );
+        out.push(
+          createTripsLayer(
+            "trips-beached-glow",
+            beachedTrips,
+            C_GLOW_BEACHED,
+            currentTimeSec,
+            trailLengthSec,
+            0.8,
+            3
+          )
+        );
+        out.push(
+          createTripsLayer(
+            "trips-beached",
+            beachedTrips,
+            C_TRAIL_BEACHED,
+            currentTimeSec,
+            trailLengthSec,
+            0.6,
+            2
+          )
+        );
+      }
+    }
+
+    if (selectedParticleId !== null) {
+      const selectedTrail = trailData.find((t) => t.id === selectedParticleId);
+      if (selectedTrail) {
+        out.push(
+          new PathLayer<TrailDatum>({
+            id: "trail-selected",
+            data: [selectedTrail],
+            getPath: (d) => d.path,
+            getColor: C_SELECTED,
+            getWidth: 3,
+            widthUnits: "pixels",
+            capRounded: true,
+            jointRounded: true,
+          })
+        );
+      }
+    }
+
+    if (showActiveParticles && activePts.length) {
+      out.push(
+        new ScatterplotLayer<PointDatum>({
+          id: "p-a",
+          data: activePts,
+          getPosition: (d) => d.position,
+          getFillColor: (d) =>
+            d.id === selectedParticleId ? C_SELECTED : activeColor(d.speed),
+          getRadius: (d) => (d.id === selectedParticleId ? 5 : 2.5),
+          radiusUnits: "pixels",
+          pickable: true,
+        })
+      );
+    }
+    if (showBeachedParticles && beachedPts.length) {
+      out.push(
+        new ScatterplotLayer<PointDatum>({
+          id: "p-b",
+          data: beachedPts,
+          getPosition: (d) => d.position,
+          getFillColor: (d) =>
+            d.id === selectedParticleId ? C_SELECTED : C_BEACHED,
+          getRadius: (d) => (d.id === selectedParticleId ? 5 : 3),
+          radiusUnits: "pixels",
+          pickable: true,
+          stroked: true,
+          lineWidthMinPixels: 1,
+          getLineColor: [255, 255, 255, 80],
+        })
+      );
+    }
+    return out;
+  }, [
+    currentFrame,
+    trailData,
+    tripDataWithTime,
+    activePts,
+    beachedPts,
+    currentTimeSec,
+    trailLengthSec,
+    selectedParticleId,
+    showTrails,
+    showActiveParticles,
+    showBeachedParticles,
+    meta,
+  ]);
+}
--- a/frontend/src/hooks/useMetadata.ts
+++ b/frontend/src/hooks/useMetadata.ts
@ -0,0 +1,17 @@
+import { useEffect, useState } from "react";
+import { API } from "@/lib/constants";
+import type { Meta } from "@/types/trajectory";
+
+export function useMetadata(simId: string = "default"): Meta | null {
+  const [meta, setMeta] = useState<Meta | null>(null);
+
+  useEffect(() => {
+    const params = new URLSearchParams({ sim: simId });
+    fetch(`${API}/api/metadata?${params}`)
+      .then((r) => r.json())
+      .then(setMeta)
+      .catch(console.error);
+  }, [simId]);
+
+  return meta;
+}
--- a/frontend/src/hooks/useSimulation.ts
+++ b/frontend/src/hooks/useSimulation.ts
@ -0,0 +1,180 @@
+import { useCallback, useEffect, useRef, useState } from "react";
+import { SPEEDS } from "@/lib/constants";
+import type { Meta } from "@/types/trajectory";
+
+/** Format current time from step when time_start/time_end exist (calendar display). When dt_hours === 1, one step = one hour (hora punta). */
+function getTimeFromStep(
+  step: number,
+  maxStep: number,
+  timeStart: string,
+  timeEnd: string,
+  dtHours?: number
+): { day: number; hour: number; dateLabel: string; startLabel: string; endLabel: string } {
+  const start = new Date(timeStart).getTime();
+  const end = new Date(timeEnd).getTime();
+  const t =
+    maxStep <= 0
+      ? start
+      : dtHours === 1
+        ? start + step * 3600 * 1000
+        : start + (step / maxStep) * (end - start);
+  const d = new Date(t);
+  const hoursSinceStart = (t - start) / (1000 * 3600);
+  const day = Math.floor(hoursSinceStart / 24) + 1;
+  const hour = Math.floor(hoursSinceStart % 24);
+  const fmt = (date: Date) =>
+    date.toLocaleDateString("en-GB", { day: "numeric", month: "short", hour: "2-digit", minute: "2-digit", hour12: false });
+  return {
+    day,
+    hour,
+    dateLabel: fmt(d),
+    startLabel: fmt(new Date(start)),
+    endLabel: fmt(new Date(end)),
+  };
+}
+
+export function useSimulation(meta: Meta | null): {
+  step: number;
+  setStep: (value: number | ((prev: number) => number)) => void;
+  playing: boolean;
+  speedIdx: number;
+  togglePlay: () => void;
+  stepBack: () => void;
+  stepForward: () => void;
+  restart: () => void;
+  cycleSpeed: () => void;
+  onSlider: (value: number[]) => void;
+  maxStep: number;
+  day: number;
+  hour: number;
+  dateLabel: string | null;
+  startLabel: string | null;
+  endLabel: string | null;
+} {
+  const [step, setStep] = useState(0);
+  const [playing, setPlaying] = useState(false);
+  const [speedIdx, setSpeedIdx] = useState(1);
+  const rafRef = useRef<number | null>(null);
+  const lastStepTimeRef = useRef<number>(0);
+  const stepIntervalRef = useRef(500 / SPEEDS[1]);
+
+  const maxStep = meta ? meta.num_steps - 1 : 0;
+  const hasCalendar =
+    meta?.time_start && meta?.time_end && maxStep > 0;
+  const { day, hour, dateLabel, startLabel, endLabel } = hasCalendar
+    ? getTimeFromStep(step, maxStep, meta.time_start!, meta.time_end!, meta.dt_hours)
+    : {
+        day: Math.floor(step / 24) + 1,
+        hour: step % 24,
+        dateLabel: null as string | null,
+        startLabel: null as string | null,
+        endLabel: null as string | null,
+      };
+
+  const togglePlay = useCallback(() => {
+    setPlaying((p) => {
+      if (!p && meta && step >= meta.num_steps - 1) setStep(0);
+      return !p;
+    });
+  }, [step, meta]);
+
+  const cycleSpeed = useCallback(() => {
+    setSpeedIdx((i) => (i + 1) % SPEEDS.length);
+  }, []);
+
+  const stepBack = useCallback(() => {
+    setStep((s) => Math.max(0, s - 1));
+  }, []);
+
+  const stepForward = useCallback(() => {
+    setStep((s) => (meta ? Math.min(meta.num_steps - 1, s + 1) : s));
+  }, [meta]);
+
+  const restart = useCallback(() => {
+    setStep(0);
+    setPlaying(false);
+  }, []);
+
+  const onSlider = useCallback(
+    (value: number[]) => {
+      const raw = value[0] ?? 0;
+      const clamped = Math.max(0, Math.min(maxStep, Math.round(raw)));
+      setStep(clamped);
+    },
+    [maxStep]
+  );
+
+  useEffect(() => {
+    if (!playing || !meta) return;
+    const dtHours = meta.dt_hours;
+    const msPerStep = dtHours === 1 ? 1000 / SPEEDS[speedIdx] : 500 / SPEEDS[speedIdx];
+    stepIntervalRef.current = msPerStep;
+    lastStepTimeRef.current = performance.now();
+
+    const tick = (now: number) => {
+      const elapsed = now - lastStepTimeRef.current;
+      if (elapsed >= stepIntervalRef.current) {
+        lastStepTimeRef.current = now;
+        setStep((prev) => {
+          if (prev >= meta.num_steps - 1) {
+            setPlaying(false);
+            return prev;
+          }
+          return prev + 1;
+        });
+      }
+      rafRef.current = requestAnimationFrame(tick);
+    };
+    rafRef.current = requestAnimationFrame(tick);
+    return () => {
+      if (rafRef.current != null) cancelAnimationFrame(rafRef.current);
+    };
+  }, [playing, meta, speedIdx]);
+
+  useEffect(() => {
+    const onKeyDown = (e: KeyboardEvent) => {
+      if (
+        e.target instanceof HTMLInputElement ||
+        e.target instanceof HTMLTextAreaElement
+      )
+        return;
+      switch (e.key) {
+        case " ":
+          e.preventDefault();
+          togglePlay();
+          break;
+        case "ArrowLeft":
+          e.preventDefault();
+          stepBack();
+          break;
+        case "ArrowRight":
+          e.preventDefault();
+          stepForward();
+          break;
+        default:
+          break;
+      }
+    };
+    window.addEventListener("keydown", onKeyDown);
+    return () => window.removeEventListener("keydown", onKeyDown);
+  }, [togglePlay, stepBack, stepForward]);
+
+  return {
+    step,
+    setStep,
+    playing,
+    speedIdx,
+    togglePlay,
+    stepBack,
+    stepForward,
+    restart,
+    cycleSpeed,
+    onSlider,
+    maxStep,
+    day,
+    hour,
+    dateLabel,
+    startLabel,
+    endLabel,
+  };
+}
--- a/frontend/src/lib/constants.ts
+++ b/frontend/src/lib/constants.ts
@ -0,0 +1,127 @@
+import type { Block } from "@/types/trajectory";
+
+export const API = process.env.NEXT_PUBLIC_API_URL ?? "http://localhost:8000";
+
+export const INIT_VIEW = {
+  longitude: 2.2,
+  latitude: 41.2,
+  zoom: 7.5,
+  pitch: 0,
+  bearing: 0,
+} as const;
+
+export const SPEEDS = [0.5, 1, 2, 4, 8] as const;
+export const BLOCK_SIZE = 24;
+export const USE_ARROW = true;
+/** Load this many blocks first so the map becomes interactive quickly; rest load in background. */
+export const INITIAL_BLOCKS = 10;
+/** Max particles to draw as trails/trips (subsampling keeps perf). */
+export const MAX_TRAIL_PARTICLES = 2500;
+/** Subsample path: one point every N steps to reduce data and speed up animation. */
+export const TRAIL_STEP_STRIDE = 3;
+/** Max trail length in hours (FlowRenderer-style: shorter = streak-like). */
+export const TRAIL_LENGTH_HOURS = 12;
+/** Options for trail length (hours) in UI. */
+export const TRAIL_LENGTH_OPTIONS = [6, 12, 24, 72] as const;
+/** Options for path density: one point every N steps. */
+export const TRAIL_STRIDE_OPTIONS = [1, 2, 3] as const;
+
+export const BASEMAPS: {
+  id: string;
+  name: string;
+  url: string;
+  thumb: string;
+}[] = [
+  {
+    id: "dark",
+    name: "Dark",
+    url: "https://basemaps.cartocdn.com/gl/dark-matter-gl-style/style.json",
+    thumb: "https://placehold.co/160x100/1e293b/475569?text=Dark",
+  },
+  {
+    id: "positron",
+    name: "Light",
+    url: "https://basemaps.cartocdn.com/gl/positron-gl-style/style.json",
+    thumb: "https://placehold.co/160x100/f1f5f9/cbd5e1?text=Light",
+  },
+  {
+    id: "voyager",
+    name: "Voyager",
+    url: "https://basemaps.cartocdn.com/gl/voyager-gl-style/style.json",
+    thumb: "https://placehold.co/160x100/0c4a6e/0ea5e9?text=Voyager",
+  },
+];
+
+export type HeaderTheme = {
+  bg: string;
+  border: string;
+  text: string;
+  subtitle: string;
+  accent: string;
+  accentMuted: string;
+  card: string;
+};
+
+export const HEADER_THEMES: Record<string, HeaderTheme> = {
+  dark: {
+    bg: "bg-slate-900/92",
+    border: "border-slate-700/60",
+    text: "text-white",
+    subtitle: "text-slate-500",
+    accent: "text-teal-400",
+    accentMuted: "bg-teal-500/20 ring-teal-500/30",
+    card: "bg-slate-800/80 border-slate-700/80",
+  },
+  positron: {
+    bg: "bg-white/95",
+    border: "border-slate-200/80",
+    text: "text-slate-900",
+    subtitle: "text-slate-500",
+    accent: "text-teal-600",
+    accentMuted: "bg-teal-500/15 ring-teal-500/40",
+    card: "bg-slate-100/90 border-slate-200",
+  },
+  voyager: {
+    bg: "bg-sky-950/90",
+    border: "border-sky-800/60",
+    text: "text-white",
+    subtitle: "text-sky-200/80",
+    accent: "text-teal-300",
+    accentMuted: "bg-teal-500/25 ring-teal-400/40",
+    card: "bg-sky-900/60 border-sky-700/80",
+  },
+};
+
+export const C_BEACHED: [number, number, number, number] = [239, 68, 68, 240];
+/** Electric blue core (FlowRenderer-style), thin streamlines */
+export const C_TRAIL_ACTIVE: [number, number, number, number] = [0, 180, 255, 255];
+export const C_TRAIL_BEACHED: [number, number, number, number] = [
+  239, 68, 68, 200,
+];
+export const C_SELECTED: [number, number, number, number] = [250, 204, 21, 255];
+/** Inner glow for electric look */
+export const C_GLOW_ACTIVE: [number, number, number, number] = [0, 180, 255, 120];
+export const C_GLOW_BEACHED: [number, number, number, number] = [
+  239, 68, 68, 70,
+];
+/** Outer bloom (very soft, wide) for FlowRenderer-style halo */
+export const C_BLOOM_ACTIVE: [number, number, number, number] = [80, 200, 255, 40];
+export const C_BLOOM_BEACHED: [number, number, number, number] = [
+  255, 100, 100, 30,
+];
+
+/** Palette per origen (seed): [R, G, B], un color per zona de llançament */
+export const PALETTE_ORIGIN: [number, number, number][] = [
+  [0, 180, 255],     // blau elèctric
+  [0, 255, 200],     // cyan
+  [100, 255, 100],   // verd
+  [255, 220, 80],    // groc
+  [255, 140, 60],    // taronja
+  [255, 100, 200],   // magenta
+  [180, 120, 255],   // lila
+  [80, 240, 255],    // cel
+];
+
+export function activeColor(_speed: number): [number, number, number, number] {
+  return [0, 180, 255, 220];
+}
--- a/frontend/src/lib/trajectoryData.ts
+++ b/frontend/src/lib/trajectoryData.ts
@ -0,0 +1,137 @@
+import type { Block, Frame, PointDatum, TrailDatum, TripDatum } from "@/types/trajectory";
+import { BLOCK_SIZE, MAX_TRAIL_PARTICLES, TRAIL_STEP_STRIDE } from "./constants";
+
+export function buildScatterData(frame: Frame): PointDatum[] {
+  const out: PointDatum[] = new Array(frame.length);
+  for (let i = 0; i < frame.length; i++) {
+    const p = frame[i];
+    out[i] = {
+      position: [p[0], p[1]],
+      beached: p[4] === 1,
+      speed: Math.sqrt(p[2] * p[2] + p[3] * p[3]),
+      id: i,
+    };
+  }
+  return out;
+}
+
+export function buildTrails(
+  allBlocks: (Block | null)[],
+  currentStep: number,
+  numParticles: number,
+  releaseSteps: number[] | undefined,
+  stepStride: number = TRAIL_STEP_STRIDE
+): TrailDatum[] {
+  const out: TrailDatum[] = [];
+  const maxP = Math.min(numParticles, MAX_TRAIL_PARTICLES);
+  for (let pid = 0; pid < maxP; pid++) {
+    const releaseStep = releaseSteps?.[pid] ?? 0;
+    if (currentStep < releaseStep) continue;
+    const path: [number, number][] = [];
+    let beached = false;
+    for (let s = releaseStep; s <= currentStep; s++) {
+      const blockIdx = Math.floor(s / BLOCK_SIZE);
+      const block = allBlocks[blockIdx];
+      if (!block?.frames?.length) continue;
+      const frameIdx = s - block.step_start;
+      if (frameIdx < 0 || frameIdx >= block.frames.length) continue;
+      const p = block.frames[frameIdx][pid];
+      if (!p) continue;
+      const isFirst = s === releaseStep;
+      const isSubsample = (s - releaseStep) % stepStride === 0;
+      const isLast = s === currentStep;
+      const isBeached = p[4] === 1;
+      if (isFirst || isSubsample || isLast || isBeached) path.push([p[0], p[1]]);
+      if (isBeached) {
+        beached = true;
+        break;
+      }
+    }
+    if (path.length > 0) out.push({ path, beached, id: pid });
+  }
+  return out;
+}
+
+export function buildTripsWithTime(
+  allBlocks: (Block | null)[],
+  currentStep: number,
+  numParticles: number,
+  releaseSteps: number[] | undefined,
+  stepStride: number = TRAIL_STEP_STRIDE
+): TripDatum[] {
+  const out: TripDatum[] = [];
+  const maxP = Math.min(numParticles, MAX_TRAIL_PARTICLES);
+  for (let pid = 0; pid < maxP; pid++) {
+    const releaseStep = releaseSteps?.[pid] ?? 0;
+    if (currentStep < releaseStep) continue;
+    const path: [number, number, number][] = [];
+    let beached = false;
+    for (let s = releaseStep; s <= currentStep; s++) {
+      const blockIdx = Math.floor(s / BLOCK_SIZE);
+      const block = allBlocks[blockIdx];
+      if (!block?.frames?.length) continue;
+      const frameIdx = s - block.step_start;
+      if (frameIdx < 0 || frameIdx >= block.frames.length) continue;
+      const p = block.frames[frameIdx][pid];
+      if (!p) continue;
+      const isFirst = s === releaseStep;
+      const isSubsample = (s - releaseStep) % stepStride === 0;
+      const isLast = s === currentStep;
+      const isBeached = p[4] === 1;
+      if (isFirst || isSubsample || isLast || isBeached)
+        path.push([p[0], p[1], s * 3600]);
+      if (isBeached) {
+        beached = true;
+        break;
+      }
+    }
+    if (path.length > 0) out.push({ path, beached, id: pid });
+  }
+  return out;
+}
+
+/**
+ * Build frames from an Arrow block table. Rows must be ordered by step then particle_id.
+ * Derives numSteps from the step column so the last block (fewer than block_size steps) is correct.
+ */
+export function framesFromArrowTable(
+  table: import("apache-arrow").Table,
+  numParticles: number
+): Frame[] {
+  const n = numParticles;
+  const stepCol = table.getChild("step");
+  const lonCol = table.getChild("lon");
+  const latCol = table.getChild("lat");
+  const uCol = table.getChild("u");
+  const vCol = table.getChild("v");
+  const beachedCol = table.getChild("beached");
+  if (!stepCol || !lonCol || !latCol || !uCol || !vCol || !beachedCol || n <= 0)
+    return [];
+  const totalRows = table.numRows;
+  const minStep = stepCol.get(0) as number;
+  const maxStep = stepCol.get(totalRows - 1) as number;
+  const numSteps = maxStep - minStep + 1;
+  if (numSteps <= 0 || totalRows < numSteps * n) return [];
+  const frames: Frame[] = [];
+  for (let stepIdx = 0; stepIdx < numSteps; stepIdx++) {
+    const frame: number[][] = [];
+    for (let pid = 0; pid < n; pid++) {
+      const row = stepIdx * n + pid;
+      frame.push([
+        lonCol.get(row) as number,
+        latCol.get(row) as number,
+        uCol.get(row) as number,
+        vCol.get(row) as number,
+        (beachedCol.get(row) as number) ?? 0,
+      ]);
+    }
+    frames.push(frame);
+  }
+  return frames;
+}
+
+export function countBeached(frame: Frame): number {
+  let c = 0;
+  for (let i = 0; i < frame.length; i++) if (frame[i][4] === 1) c++;
+  return c;
+}
--- a/frontend/src/lib/utils.ts
+++ b/frontend/src/lib/utils.ts
@ -0,0 +1,6 @@
+import { clsx, type ClassValue } from "clsx"
+import { twMerge } from "tailwind-merge"
+
+export function cn(...inputs: ClassValue[]) {
+  return twMerge(clsx(inputs))
+}
--- a/frontend/src/types/trajectory.ts
+++ b/frontend/src/types/trajectory.ts
@ -0,0 +1,46 @@
+export interface Meta {
+  num_particles: number;
+  num_steps: number;
+  num_blocks: number;
+  block_size: number;
+  seed_names: string[];
+  origins: number[];
+  release_steps?: number[];
+  /** ISO datetime of first step (from NetCDF time axis). */
+  time_start?: string;
+  /** ISO datetime of last step (from NetCDF time axis). */
+  time_end?: string;
+  /** Hours per step (e.g. 1 = one sample per hour). */
+  dt_hours?: number;
+}
+
+export type Frame = number[][];
+export type Accum = number[][];
+
+export interface Block {
+  block: number;
+  step_start: number;
+  step_end: number;
+  frames: Frame[];
+  accumulation: Accum[];
+}
+
+export interface PointDatum {
+  position: [number, number];
+  beached: boolean;
+  speed: number;
+  id: number;
+}
+
+export interface TrailDatum {
+  path: [number, number][];
+  beached: boolean;
+  id: number;
+}
+
+/** For TripsLayer: path [lon, lat, timeSec], timestamps strictly increasing. */
+export interface TripDatum {
+  path: [number, number, number][];
+  beached: boolean;
+  id: number;
+}
--- a/frontend/tsconfig.json
+++ b/frontend/tsconfig.json
@ -0,0 +1,34 @@
+{
+  "compilerOptions": {
+    "target": "ES2017",
+    "lib": ["dom", "dom.iterable", "esnext"],
+    "allowJs": true,
+    "skipLibCheck": true,
+    "strict": true,
+    "noEmit": true,
+    "esModuleInterop": true,
+    "module": "esnext",
+    "moduleResolution": "bundler",
+    "resolveJsonModule": true,
+    "isolatedModules": true,
+    "jsx": "react-jsx",
+    "incremental": true,
+    "plugins": [
+      {
+        "name": "next"
+      }
+    ],
+    "paths": {
+      "@/*": ["./src/*"]
+    }
+  },
+  "include": [
+    "next-env.d.ts",
+    "**/*.ts",
+    "**/*.tsx",
+    ".next/types/**/*.ts",
+    ".next/dev/types/**/*.ts",
+    "**/*.mts"
+  ],
+  "exclude": ["node_modules"]
+}
				`@ -0,0 +1 @@`
				`# ETL: NetCDF trajectory → Apache Arrow blocks for frontend`
				`@ -0,0 +1 @@`
				`<svg fill="none" viewBox="0 0 16 16" xmlns="http://www.w3.org/2000/svg"><path d="M14.5 13.5V5.41a1 1 0 0 0-.3-.7L9.8.29A1 1 0 0 0 9.08 0H1.5v13.5A2.5 2.5 0 0 0 4 16h8a2.5 2.5 0 0 0 2.5-2.5m-1.5 0v-7H8v-5H3v12a1 1 0 0 0 1 1h8a1 1 0 0 0 1-1M9.5 5V2.12L12.38 5zM5.13 5h-.62v1.25h2.12V5zm-.62 3h7.12v1.25H4.5zm.62 3h-.62v1.25h7.12V11z" clip-rule="evenodd" fill="#666" fill-rule="evenodd"/></svg>`
				`@ -0,0 +1 @@`
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				`@ -0,0 +1 @@`
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				`@ -0,0 +1 @@`
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