feat: add native road center lines

blender/generate_scene.py

@@ -799,11 +799,11 @@ def build(args):
             target = source["material_layer"]
             layer = material_layers[target]
             source_path = os.path.join(native_road_dir, "layers", source["source"] + ".geojson")
+            if not os.path.isfile(source_path):
+                raise RuntimeError("Native road layer is missing: " + source_path)
             count = _roads.assemble_geojson_layer(
                 source_path, source["source"], projector, roads_c,
                 road_mats[target], layer["z"])
-            if count == 0:
-                raise RuntimeError("Native road layer has no usable geometry: " + source_path)
             road_counts[source["source"]] = count
     elif geojson_dir and os.path.isdir(geojson_dir):
         for problem in catalog.check_layers(geojson_dir):