pythonmatplotlibdelaunay

Getting the circumcentres from a delaunay triangulation generated using matplotlib


If I use matplotlib to generate a delaunay triangulation for a group of points, what is the most appropraite way of getting the circumcentres of the triangles that have been geenrated? I haven't yet managed to find an obvious method in the Triangulation library to do this.


Solution

  • You should be able to calculate it using matplotlib.delaunay.triangulate.Triangulation:

    Triangulation(x, y) x, y -- the coordinates of the points as 1-D arrays of floats

    . . .

    Attributes: (all should be treated as read-only to maintain consistency) x, y -- the coordinates of the points as 1-D arrays of floats.

      circumcenters -- (ntriangles, 2) array of floats giving the (x,y)
        coordinates of the circumcenters of each triangle (indexed by a triangle_id).
    

    Adapted from one of the matplotlib examples (there is probably a cleaner way to do this, but it should work):

    import matplotlib.pyplot as plt
    import matplotlib.delaunay
    import matplotlib.tri as tri
    import numpy as np
    import math
    
    # Creating a Triangulation without specifying the triangles results in the
    # Delaunay triangulation of the points.
    
    # First create the x and y coordinates of the points.
    n_angles = 36
    n_radii = 8
    min_radius = 0.25
    radii = np.linspace(min_radius, 0.95, n_radii)
    
    angles = np.linspace(0, 2*math.pi, n_angles, endpoint=False)
    angles = np.repeat(angles[...,np.newaxis], n_radii, axis=1)
    angles[:,1::2] += math.pi/n_angles
    
    x = (radii*np.cos(angles)).flatten()
    y = (radii*np.sin(angles)).flatten()
    
    tt = matplotlib.delaunay.triangulate.Triangulation(x,y)
    triang = tri.Triangulation(x, y)
    
    # Plot the triangulation.
    plt.figure()
    plt.gca().set_aspect('equal')
    plt.triplot(triang, 'bo-')
    
    plt.plot(tt.circumcenters[:,0],tt.circumcenters[:,1],'r.')
    plt.show()