idlastro / FITS Astrometry and Calibration: FITS_CD_FIX

[Source code]

NAME
FITS_CD_FIX
PURPOSE
Update obsolete representations of the CD matrix in a FITS header   
EXPLANATION
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
FITS_CD_FIX, Hdr
INPUT-OUTPUT
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
      earlier versions.
PROCEDURES USED
SXADDPAR, SXDELPAR, SXPAR()
REVISION HISTORY
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