[fitsbits] CDELTn

[William Pence]

Francois Ochsenbein wrote:
> And on my side I'm perfectly happy with whatever convention for denegerate
> axes -- I was just troubled by the fact that fv refuses a FITS file
> having a CDELTi = 0 for these degenerate axes, and was wondering why.

I was not able to reproduce this behavior in fv using either the 
previous 4.4 version, or the new 5.0 version that was just released last 
week.  Which version are you using?  Incidentally, the main new feature 
of fv 5.0 is that it now uses Calabretta's wcslib library to do all the 
WCS transformations, and thus now supports the full set of possible WCS 
projections and not just the half a dozen or so classic projections that 
were previously supported.

Even though the current version of fv does not complain if CDELTn = 0 
for a degenerate axis, the FITS WCS papers seem pretty clear that this 
is not allowed.  The proposed new FITS Standard document does mention at 
one point in the text that CDELTn must be non-zero, but this restriction 
should probably also be stated in the actual definition of the CDELTn 
keyword.

Bill
-- 
____________________________________________________________________
Dr. William Pence                       pence at milkyway.gsfc.nasa.gov
NASA/GSFC Code 662       HEASARC        +1-301-286-4599 (voice)
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