[fitsbits] Primary & Alternate WCS Keyword Order

[Phil Hodge]

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