backend: initial commit

bincio/extract/simplify.py

@@ -0,0 +1,60 @@
+"""GPS track simplification using the Ramer-Douglas-Peucker algorithm."""
+
+from typing import Optional
+
+from rdp import rdp
+
+from bincio.extract.models import DataPoint
+
+
+def simplify_track(
+    points: list[DataPoint],
+    epsilon: float = 0.0001,
+) -> list[DataPoint]:
+    """Return a simplified subset of points using RDP.
+
+    epsilon is in degrees (~11m at equator for 0.0001).
+    Points without GPS coordinates are dropped.
+    """
+    gps_pts = [(p, p.lat, p.lon) for p in points if p.lat is not None and p.lon is not None]
+    if len(gps_pts) < 2:
+        return [p for p, _, _ in gps_pts]
+
+    coords = [[lon, lat] for _, lat, lon in gps_pts]
+    mask = rdp(coords, epsilon=epsilon, return_mask=True)
+    return [p for (p, _, _), keep in zip(gps_pts, mask) if keep]
+
+
+def build_geojson(
+    points: list[DataPoint],
+    activity_id: str,
+    epsilon: float = 0.0001,
+    original_count: Optional[int] = None,
+) -> dict:
+    """Build a GeoJSON Feature for the simplified track."""
+    simplified = simplify_track(points, epsilon=epsilon)
+
+    coordinates = [
+        [p.lon, p.lat, p.elevation_m] if p.elevation_m is not None else [p.lon, p.lat]
+        for p in simplified
+        if p.lon is not None and p.lat is not None
+    ]
+
+    # Parallel speed array for gradient coloring
+    speeds = [round(p.speed_kmh, 2) if p.speed_kmh is not None else None for p in simplified]
+
+    return {
+        "type": "Feature",
+        "geometry": {
+            "type": "LineString",
+            "coordinates": coordinates,
+        },
+        "properties": {
+            "id": activity_id,
+            "speeds": speeds,
+            "simplification": "rdp",
+            "rdp_epsilon": epsilon,
+            "point_count_original": original_count or len(points),
+            "point_count_simplified": len(coordinates),
+        },
+    }