[fitsbits] Proposed Changes to the FITS Standard

[Rob Seaman]

William Pence wrote:

> One of the proposed changes, however,  is to require that the  
> PCOUNT and GCOUNT keywords must  immediately follow the last NAXISn  
> keyword in all conforming extensions,

It seems to me that if this or any future revision to the standard is  
going to attempt to require newly defined usage that this MUST be  
paired with a version mechanism.  Otherwise "once FITS always FITS"  
is violated big time.  Requiring a feature (a demand) is not the same  
as deprecating its converse (a suggestion).  Rather, a feature that  
isn't already required can only in the future be required against  
some specially labeled subset of FITS files.

I agree with Preben that there are also problems with introducing  
versioning, but otherwise conformance is unenforceable.  The  
suggested new wording of 3.7:

	‘Existing FITS files that conformed to the latest
	version of the standard at the time the files were
	created are expressly exempt from any new
	requirements imposed by subsequent versions
	of the standard’.

can't serve as a substitute for an explicit version since A) not all  
files have DATE keywords, so how would you know, and B) it will take  
several years - perhaps never - for all prior software to adopt the  
new standards.  Rather, projects wanting to assert compliance would  
include a recognizable FITSVER (for example) keyword.  Files missing  
this tag would by default only claim compliance with the original  
standard.

In a real sense, the standard as revised is really a brand new  
standard, subclassed out of FITS.

- Rob