def split_coords_3d(seq):
    """
    :param seq: a flat list with lons, lats and depths
    :returns: a validated list of (lon, lat, depths) triplets

    >>> split_coords_3d([1.1, 2.1, 0.1, 2.3, 2.4, 0.1])
    [(1.1, 2.1, 0.1), (2.3, 2.4, 0.1)]
    """
    lons, lats, depths = [], [], []
    for i, el in enumerate(seq):
        if i % 3 == 0:
            lons.append(valid.longitude(el))
        elif i % 3 == 1:
            lats.append(valid.latitude(el))
        elif i % 3 == 2:
            depths.append(valid.depth(el))
    return list(zip(lons, lats, depths))
:param seq: a flat list with lons, lats and depths
    :returns: a validated list of (lon, lat, depths) triplets

    >>> split_coords_3d([1.1, 2.1, 0.1, 2.3, 2.4, 0.1])
    [(1.1, 2.1, 0.1), (2.3, 2.4, 0.1)]