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[fitsbits] CDELTn



 
 
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Old September 19th 07, 09:30 AM posted to sci.astro.fits
Francois Ochsenbein
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Default [fitsbits] CDELTn


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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