[fitsbits] Primary & Alternate WCS Keyword Order

[Phil Hodge]

On 06/22/2012 11:37 AM, Randy Thompson wrote:
> A question came up regarding the relative order of
> primary and alternate WCS keywords in a FITS header, particularly
> the WCSAXES and WCSAXESa keywords. The current standard (section 8.2)
> states that the WCSAXES keyword  "... if present, must precede all WCS
> keywords except NAXIS in the HDU." Does this mean the primary
> WCS keywords must come before the alternate WCS?
No.

> Does it also imply
> that the alternate WCSAXESa keyword must come before the other primary
> WCS keywords or only before the alternate WCS..a keywords?
No.  If the rule about WCSAXES preceding all other WCS keywords applied 
to WCSAXESa, then WCSAXESa would have to come before WCSAXES, and 
WCSAXES must come before WCSAXESa for the same reason.

Phil