@classmethod
def init_and_get_iter(cls, mirror_rp, inc_rp, compare_time):
    """Return rorp iter at given compare time"""
    cls.set_mirror_and_rest_times(compare_time)
    cls.initialize_rf_cache(mirror_rp, inc_rp)
    return cls.subtract_indices(cls.mirror_base.index, cls.
        get_mirror_rorp_iter())
