[fitsbits] Primary & Alternate WCS Keyword Order

[Randy Thompson]

>From our experience and according to the project
producing them, there have not been any
user-reported problems with reading these files.
They were first made public in January.

Randy


On 6/22/12 3:43 PM, "Phil Hodge" <hodge at stsci.edu> wrote:

>On 06/22/2012 01:42 PM, William Pence wrote:
>> I think Randy's question boils down to 2 possible interpretations of the
>> requirement in Section 8.2 of the FITS Standard that the WCSAXIS
>> keyword, "if present,*must*  precede all WCS keywords except NAXIS in
>> the HDU".  Does this mean that*all*  the WCSAXES/WCSAXESn keyword must
>> precede*all*  the other WCS keywords, or does it only mean that each
>> WCSAXESa keyword must precede all the other WCS keywords for that same
>> alternate system (as given by the 'a' suffix).
>
>What is the purpose of the requirement?  Is it so a reader of WCS
>keywords can read the header in a single pass, allocating memory for
>keyword arrays based on WCSAXESa, or NAXIS if WCSAXESa is not found?  If
>so, it would seem sufficient to me that the WCSAXESa keyword precede all
>other WCS keywords for alternate system 'a' only, rather than having to
>precede WCS keywords for the primary as well as any other alternate
>WCS.  Is there a WCS keyword reader that actually depends on WCSAXESa
>preceding any other WCS keyword (other than NAXIS), i.e. the more strict
>assumption used by fverify?
>
>Phil
>
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