def triangulate_polygon(polygon,
triangle_args=None,
engine=None,
**kwargs):
"""
Given a shapely polygon create a triangulation using a
python interface to `triangle.c` or mapbox-earcut.
> pip install triangle
> pip install mapbox_earcut
Parameters
---------
polygon : Shapely.geometry.Polygon
Polygon object to be triangulated
triangle_args : str or None
Passed to triangle.triangulate i.e: 'p', 'pq30'
engine : None or str
Any value other than 'earcut' will use `triangle`
Returns
--------------
vertices : (n, 2) float
Points in space
faces : (n, 3) int
Index of vertices that make up triangles
"""
if engine == 'earcut':
from mapbox_earcut import triangulate_float64
# get vertices as sequence where exterior is the first value
vertices = [np.array(polygon.exterior)]
vertices.extend(np.array(i) for i in polygon.interiors)
# record the index from the length of each vertex array
rings = np.cumsum([len(v) for v in vertices])
# stack vertices into (n, 2) float array
vertices = np.vstack(vertices)
# run triangulation
faces = triangulate_float64(vertices, rings).reshape(
(-1, 3)).astype(np.int64).reshape((-1, 3))
return vertices, faces
# do the import here for soft requirement
from triangle import triangulate
# set default triangulation arguments if not specified
if triangle_args is None:
triangle_args = 'p'
# turn the polygon in to vertices, segments, and hole points
arg = _polygon_to_kwargs(polygon)
# run the triangulation
result = triangulate(arg, triangle_args)
return result['vertices'], result['triangles']
def triangulatePolygon_mapbox(polygon):
import mapbox_earcut
vertices, rings = [], []
ring = polygon.exterior.coords[:
-1] # despite 'ring' name, actually need a chain
vertices.extend(ring)
rings.append(len(vertices))
for interior in polygon.interiors:
ring = interior.coords[:-1]
vertices.extend(ring)
rings.append(len(vertices))
vertices = np.array(vertices, dtype=np.float64)
rings = np.array(rings)
result = mapbox_earcut.triangulate_float64(vertices, rings)
triangles = []
points = vertices[result]
its = [iter(points)] * 3
for triple in zip(*its):
triangles.append(shapely.geometry.Polygon(triple))
return triangles