[fitsbits] CDELTn

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On Thu, 20 Sep 2007, Thierry Forveille wrote:

> > The only other point is that CDELTn were around before WCS,
> Around before the WCS paper yes, but not around before WCS: [...]
> but basic WCS is much older.

I was of course referring to the WCS papers. The "basics" (CRVAL CRPIX 
CDELT and CROTA) were probably there since the very beginning (but CROTA 
was later deprecated). I am not able now to verify if any of the 
earliest (pre-WCS-paper) standards explicitly specified constraints for 
CDELT ... and hence to tell whether Francois's CDELT=0 files were once 
legal.


> > Looks a sensible suggestion. Not using degenerate axes is perhaps even
> > more sensibile :-)
> > 
> Not at all :-) Degenerate axes are actually a most natural (if perhaps
> initially slightly counterintuitive, for some) way of conveying position
> information along the missing axes. One classical example is using
> two degenerate axes to convey RA & Dec (or lII & bII, or whatever)
> information for a set of individual spectra obtained on a grid,

I was thinking of much sillier cases. People writing a 1-d spectrum as a 
FITS image (and this instead of a bintable is something I accept) as
NAXIS=2 NAXIS1=nbins NAXIS2=1


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