[fitsbits] CDELTn

[Francois Ochsenbein]

Well, my question about CDELTn=0 was not related to WCS -- a simple
multidimensional hypercube which has several NAXISn set to 1 -- a current
practice in FITS. And I'm surprised by Phil's remark:

>Regardless of the value of NAXISn, computing the coordinate value at a
>pixel would involve dividing by CDELTn.  For example:  CRVALn + (1 -
>CRPIXn) / CDELTn.  So it's not as harmless as it may seem.

... I always understood that the coordinate value is 
    CRVALn + (i-CRPIXn)*CDELTn

which simply means that the value of the coordinate along this axis
is constant and equal to CRVALn, which seems to me perfectly correct
(a 1-point dimension is by definition a constant).
The formula is not reversible, but it does not be, as far as I know.

--Francois
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Francois Ochsenbein       ------       Observatoire Astronomique de Strasbourg
   11, rue de l'Universite F-67000 STRASBOURG       Phone: +33-(0)390 24 24 29
Email: francois at astro.u-strasbg.fr   (France)         Fax: +33-(0)390 24 24 32
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