def meta_S2string(S2str):
    """ get meta information of the Sentinel-2 file name

    Parameters
    ----------
    S2str : string
        filename of the L1C data

    Returns
    -------
    S2time : string
        date "+YYYY-MM-DD"
    S2orbit : string
        relative orbit "RXXX"
    S2tile : string
        tile code "TXXXXX"

    Example
    -------
    >>> S2str = 'S2A_MSIL1C_20200923T163311_N0209_R140_T15MXV_20200923T200821.SAFE'
    >>> S2time, S2orbit, S2tile = meta_S2string(S2str)
    >>> S2time
    '+2020-09-23'
    >>> S2orbit
    'R140'
    >>> S2tile
    'T15MXV'
    """
    assert type(S2str)==str, ("please provide a string")
    assert S2str[0:2]=='S2', ("please provide a Sentinel-2 file string")
    S2split = S2str.split('_')
    S2time = S2split[2][0:8]
    # convert to +YYYY-MM-DD string
    # then it can be in the meta-data of following products
    S2time = '+' + S2time[0:4] +'-'+ S2time[4:6] +'-'+ S2time[6:8]
    S2orbit = S2split[4]
    S2tile = S2split[5]
    return S2time, S2orbit, S2tile