def offset_to_skydir(skydir, offset_lon, offset_lat,
                     coordsys='CEL', projection='AIT'):
    """Convert a cartesian offset (X,Y) in the given projection into
    a SkyCoord."""

    offset_lon = np.array(offset_lon, ndmin=1)
    offset_lat = np.array(offset_lat, ndmin=1)

    w = create_wcs(skydir, coordsys, projection)
    return SkyCoord.from_pixel(offset_lon, offset_lat, w, 0)