Determine the relative path length at each x,y position.

def _calc_relative_path_lengths(self, x, y):
        """Determine the relative path length at each x,y position."""

        path_lengths = np.sqrt(np.diff(x) ** 2 + np.diff(y) ** 2)
        total_length = np.sum(path_lengths)
        cummulative_lengths = np.cumsum(path_lengths)
        relative_path_lengths = cummulative_lengths / total_length
        return relative_path_lengths