Name

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      HREVERSE

Purpose

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      Reverse an image about either dimension and update FITS astrometry

Explanation

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

Calling Sequence

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

Inputs

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

Optional Inputs

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      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.

Optional Outputs

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      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 Keyword Input

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

Optional Keyword Output

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      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.

Side Effects

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

Procedure

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      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

Procedures Used

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

Modification History

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      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