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HROT

HROT

Name


      HROT

Purpose


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

Explanation


      Cubic, bilinear or nearest neighbor interpolation can be used.

Calling Sequence


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

Inputs


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

Optional Inputs


      NEWIM - If NEWIM is set to -1, then the old image and header will
              be updated
      ANGLE - Rotation angle, degrees clockwise, scalar
      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.

Optional Outputs


      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.

Optional Input Keyword


      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.

Optional Output Keyword


      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.

Example


      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

Restrictions


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

Procedure


      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

Procedures Used


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

Modification History


      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
      Work with angle as a 1 element vector W.L. May 2006



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