Fixing random turns

backend/api/routes.py

@@ -12,10 +12,35 @@ DISTANCE_BUDGET_FACTOR_OVERALL    = 1.5
 
 
 def route_to_geojson(G, route):
-    coordinates = [
-        [G.nodes[node]["x"], G.nodes[node]["y"]]
-        for node in route
-    ]
+    """
+    Build GeoJSON coordinates from the route node list.
+
+    For each edge, use the OSM edge geometry (intermediate curve points)
+    if available — otherwise fall back to straight start→end node coords.
+    This prevents phantom turns caused by straight-line interpolation
+    between widely-spaced nodes on curved roads.
+    """
+    if len(route) == 0:
+        coordinates = []
+    elif len(route) == 1:
+        n = route[0]
+        coordinates = [[G.nodes[n]["x"], G.nodes[n]["y"]]]
+    else:
+        coordinates = [[G.nodes[route[0]]["x"], G.nodes[route[0]]["y"]]]
+        for i in range(len(route) - 1):
+            u, v = route[i], route[i + 1]
+            edge = list(G[u][v].values())[0]
+            geom = edge.get("geometry")
+            if geom is not None:
+                # geom is a Shapely LineString — coords are (lon, lat)
+                # Skip the first point (already added as previous node)
+                pts = list(geom.coords)
+                for lon, lat in pts[1:]:
+                    coordinates.append([lon, lat])
+            else:
+                # No intermediate geometry — just add the end node
+                coordinates.append([G.nodes[v]["x"], G.nodes[v]["y"]])
+
     return {
         "type": "Feature",
         "geometry": {