move triangulate_polygon into c3nav.mapdata.utils.mesh

src/c3nav/mapdata/utils/mesh.py

@@ -0,0 +1,57 @@
+from collections import deque
+from functools import lru_cache
+from itertools import chain
+from typing import Union
+
+import numpy as np
+from meshpy import triangle
+from shapely.geometry import MultiPolygon, Polygon
+
+
+@lru_cache()
+def get_face_indizes(start, length):
+    indices = np.tile(np.arange(start, start + length).reshape((-1, 1)), 2).flatten()[1:-1].reshape((length - 1, 2))
+    return np.vstack((indices, (indices[-1][-1], indices[0][0])))
+
+
+def _triangulate_polygon(polygon: Polygon, keep_holes=False):
+    vertices = deque()
+    segments = deque()
+
+    offset = 0
+    for ring in chain((polygon.exterior,), polygon.interiors):
+        new_vertices = np.array(ring.coords)[:-1]
+        vertices.append(new_vertices)
+        segments.append(get_face_indizes(offset, len(new_vertices)))
+        offset += len(new_vertices)
+
+    info = triangle.MeshInfo()
+    info.set_points(np.vstack(vertices))
+    info.set_facets(np.vstack(segments).tolist())
+
+    if not keep_holes:
+        holes = np.array(tuple(
+            Polygon(ring).representative_point().coords for ring in polygon.interiors
+        ))
+        if holes.size:
+            info.set_holes(holes.reshape((holes.shape[0], -1)))
+
+    mesh = triangle.build(info)
+    return np.array(mesh.points), np.array(mesh.elements)
+
+
+def triangulate_polygon(geometry: Union[Polygon, MultiPolygon], keep_holes=False):
+    if isinstance(geometry, Polygon):
+        return _triangulate_polygon(geometry)
+
+    vertices = deque()
+    faces = deque()
+
+    offset = 0
+    for polygon in geometry.geoms:
+        new_vertices, new_faces = _triangulate_polygon(polygon, keep_holes=keep_holes)
+        vertices.append(new_vertices)
+        faces.append(new_faces+offset if offset else new_faces)
+        offset += len(new_vertices)
+
+    return np.vstack(vertices), np.vstack(faces)