Name

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      GSSSADXY

Purpose

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      Converts RA and DEC (J2000) to (X,Y) for an STScI GuideStar image.

Explanation

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

Calling Sequence

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      GSSSADXY, GSA, Ra,Dec, [ X, Y, /Print ]

Input

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      GSA - the GSSS Astrometry structure created by GSSSEXTAST
      RA - the RA coordinate(s) in *degrees*, scalar or vector
      DEC - the DEC coordinate(s) in *degrees*, scalar or vector

Optional Keyword Input

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

Output

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      X - the corresponding X pixel coordinate(s), double precision
      Y - the corresponding Y pixel coordinate(s), double precision
      X and Y will be in IDL convention (first pixel 0,0)

Example

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      Given a FITS header, hdr, from the STScI Guidestar Survey, determine
      the X,Y coordinates of 3C 273 (RA = 12 29 6.7 +02 03 08)
      IDL> GSSSEXTAST, hdr, gsa ;Extract astrometry structure
      IDL> GSSSADXY, gsa, ten(12,29,6.7)*15,ten(2,3,8),/print

Notes

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

Procedures Called

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      ASTDISP - Print RA, Dec in standard format

History

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      10-JUL-90 Version 1 written by Eric W. Deutsch
              Derived from procedures written by Brian McLean
      Vectorized code W. Landsman March, 1991
      14-AUG-91 Fixed error which caused returned X and Y to be .5 pixels too
              large. Now X,Y follows same protocol as ADXY.
      June 1994 - Dropped PRFLAG parameter, added /PRINT W. Landsman (HSTX)
      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
      Reduce memory requirements for large arrays D. Finkbeiner April 2004