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Cython wrapper for the Boost Voronoi library (version 1.59.0)

Project description

A wrapper for Boost’s Voronoi diagram library



Cython dependency is optional. Cpp sources generated with Cython are available in releases.

Note on using the operates in 2 modes that are based on the presence of the dev file in the root of the project.

  • When dev is present, Cython will be used to compile the .pyx sources. This is the development mode (as you get it in the git repository).
  • When dev is absent, C/C++ compiler will be used to compile the .cpp sources (that were prepared in in the development mode). This is the distribution mode (as you get it on PyPI).

This way the package can be used without or with an incompatible version of Cython.

The idea comes from Matt Shannon’s bandmat library.

From PyPI

Cython not required.

pip install pyvoronoi

From source

Cython required.

Clone the repository:

git clone


python install

After every modification of .pyx files compile with Cython:

python build_ext --inplace


Create a new instance, passing the scaling factor into the constructor: ` import pyvoronoi pv = pyvoronoi.Pyvoronoi(10) `

Since the voronoi library uses integer representation for points, the scaling factor chosen must be high enough to avoid roundoff error when converting from point coordinates to integers.

Add points and segments:

pv.AddPoint([0, 0])

Call Construct() and get the edges and vertices:

      edges = pv.GetEdges()
      vertices = pv.GetVertices()
cells = pv.GetCells()

Edges have the following properties:

  • start, end contain the indices of the start and end vertices or -1 if the edge is infinite at that end.
  • is_primary is true if the edge is not coincident with any of the source inputs.
  • is_linear is true if the edge is linear (not curved).
  • site1, site2 are the indices of the sites which generated this edge. Sites are indexed as points, then segments, so if there are 5 points and 3 segments, a site index of 7 means the last segment, a site index of 2 means the third point.
  • cell is the identifier of the cell this segment is part of.
  • twin is the identifier of the twin segment as defined in the boost voronoi API.

Cells have the following properties: * cell_identifier is the index of the cell. * site is the index of the site which generated this cell (same as site1, site2 on the edges). * contains_point is true if the site was generated by a point. * contains_segment is true if the site was generated by a segment. * is_open is true if any of the cell’s edges is infinite. * vertices contains indices into the vertex array. * edges contains indices into the edge array.

pv = pyvoronoi.Pyvoronoi(100)

edges = pv.GetEdges()
vertices = pv.GetVertices()
cells = pv.GetCells()
print("Cell Count: {0}".format(len(cells)))
for c in cells:
    print("Cell contains point: {0}. Contains segment: {1}. Is open: {2}, Site Index: {3}".format(c.contains_point, c.contains_segment, c.is_open,
    for sIndex in c.edges:
        print("Start Index: {0}, End Index = {1}".format(edges[sIndex].start, edges[sIndex].end))

Some output edges returned by the boost voronoi API are suposed to be curved. In the C++ API, it is up to you to code it. Luckily, you can do it in python using the following the function DiscretizeCurvedEdge. The sample below shows you how to do that:

for cIndex in range(len(cells)):
        cell = cells[cIndex]
        if cell.is_open == False:
                for i in range(len(cell.edges)):
                        e = edges[cell.edges[i]]
                        startVertex = vertices[e.start]
                        endVertex = vertices[e.end]

                        max_distance  = distance([startVertex.X, startVertex.Y], [endVertex.X, endVertex.Y]) / 10
                        if startVertex != -1 and endVertex != -1:
                                if(e.is_linear == True):
                                        array = [[startVertex.X, startVertex.Y],[endVertex.X, endVertex.Y]]
                                        points = pv.DiscretizeCurvedEdge(cell.edges[i], max_distance)
                                        for p in points:
                                                print "{0},{1}".format(p[0], p[1])

The code used for the discretization is a port to python of this C++ code available on the boost voronoi web site


  • Pyvoronoi is available under MIT license.
  • The core Voronoi library is available under Boost Software License. Freeware for both open source and commercial applications.

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