HCONGRID

       CONGRID an image and update astrometry in a FITS header

       Expand or contract an image using CONGRID and update the
       associated FITS header array.

       HCONGRID, oldhd                       ;Update FITS header only
       HCONGRID, oldim, oldhd, [ newim, newhd, newx, newy, /HALF_HALF
                                 CUBIC = , INTERP=, OUTSIZE=, ERRMSG=, ALT= ]

       OLDIM - the original image array
       OLDHD - the original image FITS header, string array

       NEWX - size of the new image in the X direction
       NEWY - size of the new image in the Y direction
               The OUTSIZE keyword can be used instead of the
               NEWX, NEWY parameters

       NEWIM - the image after expansion or contraction with CONGRID
       NEWHD - header for newim containing updated astrometry info
               If output parameters are not supplied, the program
               will modify the input parameters OLDIM and OLDHD
               to contain the new array and updated header.

      ALT - Single character 'A' through 'Z' or ' ' specifying which astrometry
          system to modify in the FITS header.    The default is to use the
          primary astrometry of ALT = ' '.    See Greisen and Calabretta (2002)
          for information about alternate astrometry keywords.
       CUBIC - If set and non-zero, then cubic interpolation is used.   Valid
               ranges are  -1 <= Cubic < 0.   Setting /CUBIC is equivalent to
               CUBIC = -1 and also equivalent to INTERP = 2.   See INTERPOLATE
               for more info.    Setting CUBIC = -0.5 is recommended.
       ERRMSG - If this keyword is supplied, then any error mesasges will be
               returned to the user in this parameter rather than depending on
               on the MESSAGE routine in IDL.   If no errors are encountered
               then a null string is returned.
       /HALF_HALF - Due to edge effects, the default behaviour of CONGRID is
           to introduce a slight shift in the image center.  Craig Markwardt
           (http://cow.physics.wisc.edu/~craigm/idl/misc.html) has written
           a modified version of CONGRID called CMCONGRID that when used with
           the /HALF_HALF keyword eliminates any shift.   The use of the
           /HALF keyword emulates CMCONGRID and eliminates any shift in the
           image centroid.
       INTERP   - 0 for nearest neighbor, 1 for bilinear interpolation
               (default), 2 for cubic (=-1) interpolation.
       OUTSIZE - Two element integer vector which can be used instead of the
               NEWX and NEWY parameters to specify the output image dimensions

       ERRMSG - If this keyword is supplied, then any error mesasges will be
               returned to the user in this parameter rather than depending on
               on the MESSAGE routine in IDL.   If no errors are encountered
               then a null string is returned.

       Expansion or contraction is done using the CONGRID function, unless
       HALF_HALF is set.
       The parameters BSCALE, NAXIS1, NAXIS2, CRPIX1, and CRPIX2 and
       the CD (or CDELT) parameters are updated for the new header.

       A FITS header can be supplied as the first parameter without having
       to supply an image array.   The astrometry in the FITS header will be
       updated to be appropriate to the specified image size.
       If the FITS header contains astrometry from a ST Guide Star image,
       then the astrometry will be converted to an approximately equivalent
       tangent projection before applying CONGRID.

       Congrid an 512 x 512 image array IM and FITS header H to size 300 x 300
       using cubic interpolation.   Use the HALF_HALF keyword to avoid
       a shift of the image centroid
       IDL> hcongrid, IM ,H, OUT = [300, 300], CUBIC = -0.5, /HALF
       The variables IM and H will be modified to the new image size.

       CHECK_FITS, CONGRID(), EXTAST, GSSS_STDAST, SXADDHIST,
       SXADDPAR, SXPAR(), ZPARCHECK

       Written, Aug. 1986 W. Landsman, STI Corp.
       Added interp keywords, J. Isensee, July, 1990
       Add cubic interpolation W. Landsman HSTX   January 1994
       Recognize a GSSS FITS header   W. Landsman   June 1994
       Fix case where header but not image supplied  W. Landsman  May 1995
       Remove call to SINCE_VERSION()   W. Landsman   March 1996
       Assume since IDL V3.5, add CUBIC keyword      W. Landsman   March 1997
       Update BSCALE even if no astrometry present   W. Landsman   May 1997
       Converted to IDL V5.0   W. Landsman   September 1997
       Added HALF_HALF keyword  W. Landsman  February 2000
       Added ERRMSG keyword, use double precision formatting W.L.  April 2000
       Recognize PC00n00m astrometry format  W. Landsman   December 2001
       Now works when both /INTERP and /HALF are set W. Landsman January 2002
       Fix output astrometry for non-equal plate scales for PC matrix or
       CROTA2 keyword, added ALT keyword.   W. Landsman May 2005

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