def getChunkIndex(chunk_id):
    """ given a chunk_id (e.g.: c-12345678-1234-1234-1234-1234567890ab_6_4)
    return the coordinates of the chunk. In this case (6,4)
    """
    # go to the first underscore
    n = chunk_id.find('_') + 1
    if n == 0:
        raise ValueError("Invalid chunk_id: {}".format(chunk_id))
    suffix = chunk_id[n:]

    index = []
    parts = suffix.split('_')
    for part in parts:
        index.append(int(part))

    return index