'Calculate plane equation coefficients for all unmasked triangles from
the point (x,y) coordinates and specified z-array of shape (npoints).
Returned array has shape (npoints,3) and allows z-value at (x,y)
position in triangle tri to be calculated using
z = array[tri,0]*x + array[tri,1]*y + array[tri,2].'

def calculate_plane_coefficients(self, z):

    return self.get_cpp_triangulation().calculate_plane_coefficients(z)
