Name

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      GSSSEXTAST

Purpose

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      Extract IDL astrometry structure from a ST Guide Star Survey FITS header

Explanation

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      This procedure extracts the astrometry information from a ST Guide
      Star Survey FITS header and places it in an IDL structure for
      subsequent use with GSSSxyad and GSSSadxy.

Calling Sequence

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      GSSSExtast, hdr, astr, noparams

Input

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      h - the GSSS FITS header

Output

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      astr - Structure containing the GSSS Astrometry information
              .CTYPE = ['RA---GSS','DEC--GSS']
              .CRVAL = plate center Ra, Dec (from PLTRAH, PLTRAM etc.)
              .XLL,.YLL = offsets lower lefthand corner
              .AMDX, .AMDY = 12 transformation coefficients
              .XSZ,.YSZ = X and Y pixel size in microns
              .PLTSCL = plate scale in arc sec/mm
              .PPO3, .PPO6 - orientation coefficients

Notes

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      Most users should use EXTAST rather than this procedure. EXTAST will
      call GSSSEXTAST if supplied with GSSS FITS header.

Procedures Called

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      SXPAR() - Extract parameter values from a FITS header

History

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      01-JUL-90 Version 1 written by Eric W. Deutsch
      Code derived from Software by Brian McLean
      20-AUG-91 Modified to Double Precision Variables. E. Deutsch
      June 94 Change astrometry tags to better agree with EXTAST W. Landsman
      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
      Eliminate use of obsolete !ERR W. Landsman February 2000