HROT

       Rotate an image and create new FITS header with updated astrometry.

       Cubic, bilinear or nearest neighbor interpolation can be used.

       HROT, oldim, oldhd, [ newim, newhd, angle, xc, yc, int,
                       MISSING =, INTERP =, CUBIC = , /PIVOT]

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

       NEWIM - If NEWIM is set to -1, then the old image and header will
               be updated
       ANGLE - Rotation angle, degrees clockwise
       XC    - X Center of rotation (-1 for center of image)
       YC    - Y Center of rotation (-1 for center of image)
       INT   - 0 for nearest neighbor, 1 for bilinear interpolation
               2 for cubic interpolation.

       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.

       MISSING - Set this keyword to a scalar value which will be assigned
               to pixels in the output image which do not correspond to
               existing input images (e.g if one rotates off-center).
               If not supplied then linear extrapolation is used.
               ***NOTE: A bug was introduced into the POLY_2D function in IDL
               V5.5 (fixed in V6.1) such that the MISSING keyword
               may not work properly with floating point data***
       INTERP - scalar set to either 0 (nearest neighbor interpolation),
               1 (bilinear interpolation), or 2 (cubic interpolation).
               The interpolation type can be specified by either the INTERP
               keyword or the int parameter
       CUBIC - If set and non-zero then cubic interpolation is used (see ROT),
               which is equivalent to setting INT = 2.   In IDL V5.0 and later,
                this keyword can also be set to a value between -1 and 0.
       /PIVOT - Setting this keyword causes the image to pivot around the point
               XC, YC, so that this point maps into the same point in the
               output image.  If this keyword is set to 0 or omitted, then the
               point XC, YC in the input image is mapped into the center of
               the output image.

       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.

       Rotate an image non-interactively 30 degrees clockwise.  Use
       bilinear interpolation, and set missing values to 0.
       IDL>  HROT, im_old, h_old, im_new, h_new, 30, -1, -1, 1, MIS = 0
       As above but update the input image and header and pivot about (100,120)
       IDL>  HROT, im_old, h_old, -1, -1, 30, 100, 120, 1, MIS = 0, /PIVOT

       Unlike the ROT procedure, HROT cannot be used to magnify or
       or demagnify an image. Use HCONGRID or HREBIN instead.

       The image array is rotated using the ROT procedure.
       The CD (or CROTA) and CRPIX parameters, if present in the FITS header,
       are updated for the new rotation.
       History records are also added to the header

       CHECK_FITS, EXTAST, GETOPT(), GETROT, ROT(), STRN(), SXADDPAR

       Written, Aug. 1986 W. Landsman, ST Systems Corp.
       Added MISSING keyword, W. Landsman March, 1991
       Added cubic interpolation, use astrometry structure   Feb 1994
       Removed call to SINCE_VERSION()  W. Landsman  March 1996
       Assume at least V3.5, add CUBIC parameter       W. Landsman  March 1997
       Converted to IDL V5.0   W. Landsman   September 1997
       Fix for CROTA2 defined and CDELT1 NE CDELT2, W. Landsman  November 1998
       Fix documentation  to specify clockwise rotation W. Landsman Dec. 1999
       Added /PIVOT keyword    W. Landsman  January 2000
       Added ERRMSG, Use double precision formatting, W. Landsman April 2000
       Consistent conversion between CROTA and CD matrix W. Landsman Oct 2000
       Work for both CD001001 and CDELT defined  W. Landsman   March 2001
       Recognize PC matrix astrometry  W. Landsman December 2001
       Update astrometry correctly when /PIVOT applied W. Landsman March 2002
       Update CROTA2 astrometry correctly, approximate GSSS W.L. June 2003
       Work with CD1_1, PC1_1 and CROTA keywords W. L. July 2003

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