feat: add OSM turn lane arrows

scripts/normalize-lane-arrows.py

@@ -152,7 +152,10 @@ def normalize_file(input_path, tolerance):
     with input_path.open("r", encoding="utf-8") as handle:
         collection = json.load(handle)
 
-    for index, feature in enumerate(collection.get("features", [])):
+    collection["features"] = merge_custom_turn_lane_arrow_components(
+        collection.get("features", [])
+    )
+    for index, feature in enumerate(collection["features"]):
         geometry = ogr.CreateGeometryFromJson(json.dumps(feature.get("geometry", {})))
         if geometry is None or geometry.IsEmpty():
             raise ValueError(f"feature {index} has no usable geometry")
@@ -171,6 +174,49 @@ def normalize_file(input_path, tolerance):
     temp_path.replace(input_path)
 
 
+def merge_custom_turn_lane_arrow_components(features):
+    """Restore each imported SVG icon before QGIS assigns its single outline."""
+    grouped = {}
+    for feature in features:
+        properties = feature.get("properties", {})
+        arrow_id = properties.get("custom_arrow_id")
+        if properties.get("source") == "osm_turn_lanes" and arrow_id:
+            grouped.setdefault(arrow_id, []).append(feature)
+
+    merged_ids = set()
+    output = []
+    for feature in features:
+        properties = feature.get("properties", {})
+        arrow_id = properties.get("custom_arrow_id")
+        if properties.get("source") != "osm_turn_lanes" or not arrow_id:
+            output.append(feature)
+            continue
+        if arrow_id in merged_ids:
+            continue
+        merged_ids.add(arrow_id)
+        components = grouped[arrow_id]
+        multi = ogr.Geometry(ogr.wkbMultiPolygon)
+        for component in components:
+            geometry = ogr.CreateGeometryFromJson(
+                json.dumps(component.get("geometry", {}))
+            )
+            if geometry is None or geometry.IsEmpty() or geometry.GetGeometryName() != "POLYGON":
+                raise ValueError(f"custom arrow {arrow_id} has an invalid component")
+            multi.AddGeometry(geometry)
+        united = multi.UnionCascaded()
+        if united is None or united.IsEmpty() or united.GetGeometryName() != "POLYGON":
+            raise ValueError(
+                f"custom arrow {arrow_id} components did not form one Polygon"
+            )
+        merged = dict(components[0])
+        merged["properties"] = dict(components[0].get("properties", {}))
+        merged["properties"].pop("arrow_part", None)
+        merged["properties"]["component_count"] = len(components)
+        merged["geometry"] = json.loads(united.ExportToJson())
+        output.append(merged)
+    return output
+
+
 def main():
     args = cli_args()
     if args.outline_simplify_meters < 0: