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