FITS_CD_FIX

    Update obsolete representations of the CD matrix in a FITS header

    According the paper, "Representations of Celestial Coordinates in FITS"
    by Calabretta & Greisen (2002, A&A, 395, 1077, available at
    http://www.aoc.nrao.edu/~egreisen/) 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.

    FITS_CD_FIX, Hdr

       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.

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

    SXADDPAR, SXDELPAR, SXPAR()

    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

[Home Page] [Software, Documentation] [IDL Documentation] [Quick Reference] [Feedback]