def METHOD_NAME(self, delta, new_delta):
    """
    gives the norm of the (delta-new_delta)
    """
    diff = delta.view(dtype=world_point_type).reshape(-1, 3)
    diff -= new_delta.view(dtype=world_point_type).reshape(-1, 3)
    return np.sum(diff ** 2, axis=1) ** .5