Editing voronoi class to return polygon points in python

Question

Would anyone with Python experience be able to take a look at this for me?

I'm using this code:

https://bitbucket.org/mozman/geoalg/src/5bbd46fa2270/geoalg/voronoi.py

to perform voronoi tesselation on a group of points.

It works, but the problem is that the code only provides a list of all the vertices used to create the polygons, and which pairs must be joined together. It doesn't provide any information as to what points are used to make up each polygon, which I need.

Thanks.

Answer 1

context.triangles says in which Delaunay triangles input point participate. Each triangle is related to a Voronoi vertex. Triangles and vertices are stored parallel in triangles and vertices arrays.

To find Voronoi cell for a given point p, it is needed to find all vertices (triangles) in which input point is used. And than find order how these vertices are connected by edges array.

Here is a simple (not quite tested) code to do that:

from voronoi import voronoi
import random
from collections import defaultdict

num_points = 50
points = [(random.uniform(0,10), random.uniform(0,10)) for i in xrange(num_points)]
c = voronoi(points)

# For each point find triangles (vertices) of a cell
point_in_triangles = defaultdict(set)
for t_ind, ps in enumerate(c.triangles):
    for p in ps:
        point_in_triangles[p].add(t_ind)

# Vertex connectivity graph
vertex_graph = defaultdict(set)
for e_ind, (_, r, l) in enumerate(c.edges):
    vertex_graph[r].add(l)
    vertex_graph[l].add(r)

def cell(point):
    if point not in point_in_triangles:
        return None
    vertices = set(point_in_triangles[point]) # copy
    v_cell = [vertices.pop()]
    vertices.add(-1)  # Simulate infinity :-)
    while vertices:
        neighbours = vertex_graph[v_cell[-1]] & vertices
        if not neighbours:
            break
        v_cell.append(neighbours.pop())
        vertices.discard(v_cell[-1])
    return v_cell

for p in xrange(num_points):
    print p, cell(p)