[fitsbits] Primary & Alternate WCS Keyword Order

[William Pence]

Regarding the ordering of FITS header keywords, it's interesting to note 
that other than the 9 mandatory structural FITS keywords that must 
appear in a specific order (SIMPLE, XTENSION, BITPIX, NAXIS, NAXISn, 
PCOUNT, GCOUNT, TFIELDS, and END), WCSAXES is the only other keyword 
defined in the FITS Standard that has any restrictions on the position 
that it can have in the header.   Maybe this requirement was useful back 
in the days of having to read FITS files sequentially off of magnetic 
tape, but now I think it is hard to justification why this one keyword 
should have this special positional requirement?

-Bill

On 06/26/2012 02:22 PM, Steve Allen wrote:
> On 2012 Jun 26, at 10:00, William Pence wrote:
>> Alternatively, why not just eliminate this requirement entirely, by
>> deleting this sentence: "This keyword, if present, must precede all WCS
>> keywords except NAXIS in the HDU."  What is the purpose and benefit of
>> this requirement?
>
> I'm pretty sure I have some correspondence with Eric and Mark when
> that section of WCS paper 1 was being polished, but I'd have to
> go digging to see if this was mentioned.  I am hoping that Mark
> will chime in on this ordering requirement.
>
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____________________________________________________________________
Dr. William Pence                       William.Pence at nasa.gov
NASA/GSFC Code 662       HEASARC        +1-301-286-4599 (voice)
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