[fitsbits] CDELTn

[Francois Ochsenbein]

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                       pence at milkyway.gsfc.nasa.gov
>NASA/GSFC Code 662       HEASARC        +1-301-286-4599 (voice)
>Greenbelt MD 20771                      +1-301-286-1684 (fax)
>
>
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Francois Ochsenbein       ------       Observatoire Astronomique de Strasbourg
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Email: francois at astro.u-strasbg.fr   (France)         Fax: +33-(0)390 24 24 32
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