James Gregson's Website

Nov 05, 2019

Useful Mesh Functions in Python

These are collections of functions that I end up re-implementing frequently.

import numpy as np

def manifold_mesh_neighbors( tris: np.ndarray ) -> np.ndarray:
    """Returns an array of triangles neighboring each triangle

        tris (Nx3 int array): triangle vertex indices

        nbrs (Nx3 int array): neighbor triangle indices,
            or -1 if boundary edge
    if tris.shape[1] != 3:
        raise ValueError('Expected a Nx3 array of triangle vertex indices')

    e2t = {}
    for idx,(a,b,c) in enumerate(tris):
        e2t[(b,a)] = idx
        e2t[(c,b)] = idx
        e2t[(a,c)] = idx

    nbr = np.full(tris.shape,-1,int)
    for idx,(a,b,c) in enumerate(tris):
        nbr[idx,0] = e2t[(a,b)] if (a,b) in e2t else -1
        nbr[idx,1] = e2t[(b,c)] if (b,c) in e2t else -1
        nbr[idx,2] = e2t[(c,a)] if (c,a) in e2t else -1
    return nbr

if __name__ == '__main__':
    tris = np.array((
    nbrs = manifold_mesh_neighbors( tris )

    tar = np.array((
    if not np.allclose(nbrs,tar):
        raise ValueError('uh oh.')