How to compute Straight Skeletons using Python?

Question

Is there a Python package which provides an implementation of a Straight Skeleton algorithm?

I'm aware that the open source (C++) project CGALcontains an implementation but it seems like cgal-bindings doesn't include this CGAL package.

In any case, I would prefer a pure Python implementation which I could modify/extend to suit my needs.

While an implementation that can handle polygons with holes would be preferable, it's not strictly necessary.

Answer 1

Maybe you can modify pySkeleton by Olivier Teboul to suit your needs.

I haven't had the chance to look at the actual code but from what he says it should be pure Python.

Answer 2

You can use pySkeleton as follows:

from pySkeleton import polygon

vertices = [(0,0), (0,5), (5,5), (5,0)]
edges = [(0,1), (1,2), (2,3), (3,0)]

p = polygon.Polygon(vertices, edges)
skeleton_graph = p.straight_skeleton()

You get a Graph-Object with Nodes and Arcs, which you can access simply by:

nodes = skeleton_graph.nodes
arcs = skeleton_graph.arcs

As it says in the pySkeleton readme.txt, the polygon vertices needs to be in clockwise-order. For holes within the polygon, vertices needs to be in counter clockwise-order.

vertices = [(25.0, 15.0), (45.0, 15.0), (45.0, 35.0), (25.0, 35.0), # polygon
            (30.0, 20.0), (30.0, 30.0), (40.0, 30.0), (40.0, 20.0)] # hole in polygon

edges = [(0, 1), (1, 2), (2, 3), (3, 0), # polygon
         (4, 5), (5, 6), (6, 7), (7, 4)] # hole in polygon

Remark: For more complex polygons with 100+ vertices and edges pySkeleton is unfeasibly slow. Besides that I receive strange results for some polygons. I assume that it does not work correctly in all cases.

Nonetheless, big thanks to Olivier Teboul for this library.