GSSSXYAD

       Convert (X,Y) coordinates in a STScI Guide Star image to RA and Dec

       The sky coordinates may be printed and/or returned in variables.

       GSSSxyad, gsa, x, y, ra, dec, [ /PRINT ]

       GSA  - The GSSS Astrometry structure extracted from a FITS header
              by GSSSEXTAST
       X - The X pixel coordinate(s) of the image, scalar or vector
       Y - The Y pixel coordinate(s) of the image, scalar or vector

       RA - The RA coordinate of the given pixel(s) in *degrees*
       DEC - The DEC coordinate of the given pixel(s) in *degrees*
       Both RA and Dec will be returned as double precision

       /PRINT - If this keyword is set and non-zero, then coordinates will be
               displayed at the terminal

       Given a FITS header,hdr, from a GSSS image, print the astronomical
       coordinates of (X,Y) = (200.23, 100.16) at the terminal
       IDL> GSSSExtast, hdr, gsa        ;Extract astrometry structure
       IDL> GSSSxyad, gsa, 200.23, 100.16, /print

       For most purpose users can simply use XYAD, which will call GSSSXYAD
       if it is passed a GSSS header.

       ASTDISP - print RA, Dec in a standard format

       01-JUL-90 Version 1 written by Eric W. Deutsch
       Vectorized Code   W. Landsman        March, 1991
       14-AUG-91 Fixed error which caused returned RA and DEC to be off by
       -.5 pixels in both X,Y.  Now X,Y follows same protocol as ADXY.
       20-AUG-91 Modified to use AstDisp procedure.
       June 94 Added /PRINT keyword instead of PRFLAG W. Landsman June 94
       Converted to IDL V5.0   W. Landsman   September 1997
       29-JUN-99 Added support for AMD[X,Y]1[2-3] for DSS images by E. Deutsch

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