Name

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    FITS_CD_FIX

Purpose

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    Update obsolete representations of the CD matrix in a FITS header

Explanation

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    According the paper, "Representations of Celestial Coordinates in FITS"
    by Calabretta & Greisen (2002, A&A, 395, 1077, available at
    http://fits.gsfc.nasa.gov/fits_wcs.html) the rotation of an image from
    standard coordinates is represented by a coordinate description (CD)
    matrix. The standard representation of the CD matrix are PCn_m
    keywords, but CDn_m keywords (which include the scale factors) are
    also allowed. However, earliers drafts of the standard allowed the
    keywords forms CD00n00m and PC00n00m. This procedure will convert
    FITS CD matrix keywords containing zeros into the standard forms
    CDn_m and PCn_m containing only underscores.

Calling Sequence

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    FITS_CD_FIX, Hdr

Input-output

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      HDR - FITS header, 80 x N string array. If the header does not
          contain 'CD00n00m' or 'PC00n00m' keywords then it is left
          unmodified. Otherwise, the keywords containing integers are
          replaced with those containing underscores.
 

Optional Keyword Input

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      /REVERSE - this keyword does nothing, but is kept for compatibility with
            earlier versions.

Procedures Used

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    SXADDPAR, SXDELPAR, SXPAR()

Revision History

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    Written W. Landsman Feb 1990
    Major rewrite Feb 1994
    Converted to IDL V5.0 W. Landsman September 1997
    Use double precision formatting of CD matrix W. Landsman April 2000
    Major rewrite to convert only to forms recognized by the Greisen
      & Calabretta standard W. Landsman July 2003