Returns the indices that would sort a list of 2D points in anticlockwise order
    :param pps: List of points to be sorted
    :return: Indices of the sorted list of points

def anticlockwise_sort_indices(pps):
    """
    Returns the indices that would sort a list of 2D points in anticlockwise order
    :param pps: List of points to be sorted
    :return: Indices of the sorted list of points
    """
    angles = np.zeros(len(pps), np.float)
    for ipp, pp in enumerate(pps):
        angles[ipp] = np.arctan2(pp[1], pp[0])
    return np.argsort(angles)