The world coordinate system (WCS) currently associated with an image may often be a celestial coordinate system, but this need not necessarily be the case. For instance, instead of right ascension and declination, an image might have a WCS with axes representing wavelength and slit position, or maybe just plain old pixels.
If you have obtained a WCS calibration for an image, as in
, in the form of a pointer WCSINFO to a
FrameSet, then you may determine if the current coordinate system is a
celestial one or not, as follows:
INTEGER FRAME
LOGICAL ISSKY
...
* Obtain a pointer to the current Frame and determine if it is a
* SkyFrame.
FRAME = AST_GETFRAME( WCSINFO, AST__CURRENT, STATUS )
ISSKY = AST_ISASKYFRAME( FRAME, STATUS )
CALL AST_ANNUL( FRAME, STATUS )
This will set ISSKY to .TRUE. if the WCS is a celestial coordinate system, and to .FALSE. otherwise.
AST A Library for Handling World Coordinate Systems in Astronomy