[fitsbits] WCSAXES usage

[William Pence]

I'm in the process of updating the FITS verifier code to deal with 
changes in version 3 of the FITS Standard, and have a question about the 
correct usage of the WCSAXES keyword: is this keyword optional in cases 
where the WCS has more axes than specified by the NAXIS keyword, as in 
the following fragment of a FITS image header:

NAXIS  = 2
NAXIS1 = 512
NAXIS2 = 512
CRPIX1 = 256
CRPIX2 = 256
CRPIX3 = 1
...

Should the FITS verifier issue a warning in this case (where there is no 
WCSAXES keyword) that the index on the CRPIX3 keyword is greater than 
the NAXIS keyword value?

The FITS Standard states that the default value for the WCSAXES keyword, 
if it is not physically present, is "NAXIS, or largest of WCS indexes i 
or j".  This suggests that the above example header is legal, and that 
the default value of WCSAXES is 3 this case.  If this is the correct 
interpretation, then the FITS verifier should not issue a warning in 
this case.

Bill
-- 
____________________________________________________________________
Dr. William Pence                       William.Pence at nasa.gov
NASA/GSFC Code 662       HEASARC        +1-301-286-4599 (voice)
Greenbelt MD 20771                      +1-301-286-1684 (fax)