[fitswcs] NAXIS vs. WCSDIM

[William Pence]

Doug Mink wrote:
> 
> I have been dealing with WCS's independent of images, Doug Tody's case I,
> for quite some time.  Sometimes I need to fit a WCS to a set of pixel values
> in a separate file and create an output file which can be used for pixel to
> sky and sky to pixel conversions.  Since no image is really necessary, I have
> included in my WCSTools package a progam to create a header-only FITS file,
> with NAXIS=w and BITPIX=0.  This works as well as having a separate keyword,
> but it requires software that doesn't crash on a heretofore illegal BITPIX
> value.

Yikes.  Producing FITS files with an illegal BITPIX value (the FITS standard
is very unambiguous about the allowed values) ought to be a last resort,
when there is no other reasonable solution that conforms to existing
standards.  Why not use NAXISn = 0 and a legal BITPIX value in your output
files?  The pixel to sky and sky to pixel conversions don't depend on the
number of pixels actually in the image do they?

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