This attribute gives the indices of the longitude and latitude
coordinates of the FITS-WCS projection within the coordinate
space used by a WcsMapWcsMap. These indices are defined when the
WcsMap is first created using astWcsMapastWcsMap and cannot
subsequently be altered.
If "lonlat" is 1, the index of the longitude axis is
returned. Otherwise, if it is 2, the index of the latitude axis
is returned.