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      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.

Calling Sequence

      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

Optional Keyword Input

      /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.

Procedures Called

      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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