GETROT

     Return the rotation and plate scale of an image from its FITS header

     Derive the counterclockwise rotation angle, and the X and Y scale
     factors of an image, from a FITS image header.   Input parameter
     may be either a FITS image header or an astrometry structure (as
     obtained by EXTAST.PRO)

     GETROT, Hdr, [ Rot, CDelt, /SILENT, DEBUG =  ]
             or
     GETROT, Astr, Rot, CDelt, /SILENT, DEBUG = ]

     HDR - FITS Image header (string array).  Program will extract the
             astrometry structure
              or
     ASTR -  ASTROMETRY structure, of the type returned by EXTAST.
             See the documentation for EXTAST.PRO for details.

       ROT - Scalar giving the counterclockwise rotation of NORTH in DEGREES
               from the +Y axis of the image.
       CDELT- 2 element vector giving the scale factors in DEGREES/PIXEL in
               the X and Y directions.   CDELT[1] is always positive, whereas
               CDELT[0] is negative for a normal left-handed coordinate system,
               and positive for a right-handed system.
       If no output variables are supplied (or /DEBUG is set), then GETROT
       will display the rotation and plate scale at the terminal.

       ALT - single character 'A' through 'Z' or ' ' specifying an alternate
             astrometry system present in the FITS header.   See extast.pro
             for more information on the ALT keyword.    Ignored if an
             astrometry structure rather than FITS header is supplied.
       DEBUG - if DEBUG is set, GETROT will print the rotation for both the
           X and Y axis when these values are unequal.  If DEBUG is set to 2,
           then the output parameter ROT will contain both X and Y rotations.
       /SILENT - if set, then do not provide a warning about a right-handed
           coordinate system

       If the FITS header already contains CDELT (and CD or CROTA) keyword,
       (as suggested by the Calabretta & Greisen (2002, A&A, 395, 1077) FITS
       standard) then this is used for the scale factor.
       If the header contains CD keywords but no CDELT keywords (as in IRAF
       headers) then the scale factor is derived from the CD matrix.

       EXTAST, GSSS_EXTAST

       Written W. Landsman STX January 1987
       Convert to IDL V2. M. Greason, STX, May 1990
       Option to return both rotations added.  J. D. Offenberg, STX, Aug 1991
       Use new astrometry structure   W. Landsman  Mar 1994
       Recognize a GSSS header        W. Landsman  June 1994
       Converted to IDL V5.0   W. Landsman   September 1997
       Correct rotation determination with unequal CDELT values WL October 1998
       Consistent conversion between CROTA and CD matrix  WL  October 2000
       Correct CDELT computations for rotations near 90 deg WL November 2002
       Preserve sign in the CDELT output  WL June 2003
       Check if latitude/longitude reversed in CTYPE  WL  February 2004
       Fix problem in latitude check  M.Lombardi/W.Landsman Sep 2004
       Added ALT keyword W. Landsman May 2005

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