HREVERSE

       Reverse an image about either dimension and update FITS astrometry

       Reverse an image about either the X or Y axis, and create a new
       header with updated astrometry for the reversed image.

       HREVERSE,oldim,oldhd, [ subs, /SILENT ]   ;Update input image and header
               or
       HREVERSE, oldim, oldhd, newim, newhd, [ subs, /SILENT ]

       OLDIM - the original image array
       OLDHD - the original image header

       SUBS - Subs equals 1 to reverse the order of the X dimension,
               2 to reverse Y order.  If omitted, then HREVERSE will
               prompt for this scalar parameter.

       NEWIM - the rotated image, with the same dimensions as Oldim
       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 rotated image and updated header.

       SILENT - if set and non-zero, then informative messages are suppressed.

       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.

       A right-handed coordinate system is converted into a left-
       handed one, and vice-versa.

       The User's Library procedure REVERSE is used to reverse the image.
       The CD and CRPIX header parameters are updated for the new header.
       For AIPS type astrometry, the CDELT parameters are also updated.
       A history record is also added to the header

       CHECK_FITS, EXTAST, REVERSE(), STRN(), SXADDPAR

       Written, Aug. 1986 W. Landsman, STI Corp.
       Error modifying CROTA angles corrected     9-23-88
       Added format keyword, J. Isensee, July, 1990
       Work for ST Guide Star images, W. Landsman   HSTX, May 1995
       Compute CRPIX1 correctly for X reversal   W. Landsman HSTX August 1995
       Converted to IDL V5.0   W. Landsman   September 1997
       Added ERRMSG, Use double precision formatting, W. Landsman April 2000
       Recognize PC00n00m astrometry matrix   W. Landsman   December 2001

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