Compute the edge-lengths of each triangle in the triangulation.

def edge_lengths(self):
        """
        Compute the edge-lengths of each triangle in the triangulation.
        """

        simplex = self.simplices.T

        # simplex is vectors a, b, c defining the corners
        a = self.points[simplex[0]]
        b = self.points[simplex[1]]
        c = self.points[simplex[2]]

        ## dot products to obtain angles
        ab = np.arccos((a * b).sum(axis=1))
        bc = np.arccos((b * c).sum(axis=1))
        ac = np.arccos((a * c).sum(axis=1))

        ## As this is a unit sphere, angle = length so ...

        return ab, bc, ac