On 26 November 2010 19:04, Jean-Baptiste Marquette <[log in to unmask]> wrote:
> Le 23 nov. 2010 à 12:00, David Berry a écrit :
>
>>>>>> Standardization urgently needed...
>>>>
>>>> And has been for years!
>>>>
>>>>> The plan was for ASTROM to be modified once the FITS Paper IV standard was finalised. It hasn't been so there is very little that can be done about it. As I said though, maybe David or whoever (who are in the UK) can comment further.
>>>>
>>>> Maybe the time is coming for the community to adopt a de facto
>>>> standard. In the mean time, only applications based on the AST library
>>>> (which includes all the starlink apps) will intepret the QV headers.
>>>
>
>
> Hi,
>
> Further to this discussion, it seems that FITS standard enters a new era with the publication of
>
> Pence et al. Definition of the Flexible Image Transport System (FITS), version 3.0. Astronomy and Astrophysics (2010) vol. 524 pp. 42
>
> At first glance, the PV keywords become standard for non-linear algorithms.
> May you comment ?
PV keywords have been standard since the publication of FITS-WCS paper
2. This paper doesn't change anything - it's just a summary of
previously agreed standards. The important point is that there is
still no agreed standard for representing post-projection distortions.
In the published standard, the PV keywords are used to describe the
parameters of the standard non-linear projections - *without
distortion*.
An early draft of FITS-WCS paper 2 included a "TAN + distortion"
projection, but this was removed before publication because general
opinion seemed to be that the distortion issue should be dealt with
more generally in a separate paper, rather than being added to one
specific projection (TAN). But the AST library adopted this draft
"TAN+distortion" projection as an interim stop-gap measure. But the PV
parameters that were initially used to describe the properties of this
distortion had subsequently been reserved for other purposes. So AST
had to invent a new set of keywords, called QV, to perform the
functions that the PV keywords used to perform in the draft paper 2.
I hope this clears things up.
David
>
> ================================================
> Bien cordialement/Very truly yours/Mit freundlichen Gruessen,
> Jean-Baptiste Marquette
> Institut d'Astrophysique de Paris
> CNRS - UMR 7095
> Université Pierre & Marie Curie
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> 75014 Paris - France
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