[fitsbits] CDELTn

Hi Bill,

I'm not sure about the version of fv I was running -- it's on a
linux and fv -help does not show the version.
I just downloaded the last version (fv5.0) and the problem does
not exist any more -- it does accept silently the CDELTi = 0.
And it also looks faster -- congratulations !

Sorry for the trouble. I understand the usefulness of degenerate axes
(to specify some important parameters) and it seems the developers
did not pay attention to this restriction -- which I feel is not
relevant for degenerate axes.

Thank you,
Francois


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
NASA/GSFC Code 662 HEASARC +1-301-286-4599 (voice)
Greenbelt MD 20771 +1-301-286-1684 (fax)


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