def srf_dxy(srf):
    """
    Retrieve SRF dx and dy.
    Assumes all planes have same dx, dy.
    srf: SRF file path to read from
    """
    with open(srf, "r") as sf:
        # version
        sf.readline()
        # planes definition
        sf.readline()
        # first plane
        elon, elat, nstk, ndip, length, width = sf.readline().split()
    return (
        float("%.2f" % (float(length) / int(nstk))),
        float("%.2f" % (float(width) / int(ndip))),
    )