[fitsbits] start of Public Comment Period on blank header space convention

[William Thompson]

On 06/26/15 13:57, Erik Bray wrote:

> I would argue that it mixing in usage "conventions" with the "dry recitation of
> the legal structure of a FITS file" makes it harder to actually read the
> documentation that is supposed to tell you about the legal structure of a FITS
> file.  I'd have no problem with an appendix or separate section about known
> usage conventions, but I would prefer that the main text of the standard stick
> to implementation details (which don't necessarily even have to be "dry"--I'm
> all for a little humor mixed in too so long as it doesn't hinder precision in
> the communication :)

At one point there was some discussion about publishing a separate companion 
document to the standard describing "officially recognized" conventions.  To me, 
that would be a sensible alternative for many of the conventions being discussed 
here.  That would be basically the same as publishing them as appendices

Another important point is that many of the conventions depend on new keywords 
that are defined as part of the convention.  It would be good to at least have 
these keywords reserved.  That might be best done by listing them in a table as 
being reserved for the usages described in the appendices or separate document.

The one convention that I would argue *should* be made part of the standard 
itself is the compressed image convention.  In my view, that's much more 
fundamental to the underlying structure of the FITS file.  Unlike the other 
conventions being discussed here, compressed images (and tables) cannot be read 
even at a basic level by software which does not support the convention.

In some sense, the CONTINUE long string convention also pertains to the 
underlying structure of the FITS file in that it specifies how the header should 
be read, as opposed to how the data should be used.  However, software which did 
not support the CONTINUE convention would still be able to read the FITS file at 
a basic level, so long as the convention was not used for keywords such as TDIMn.

Bill Thompson

-- 
William Thompson
NASA Goddard Space Flight Center
Code 671
Greenbelt, MD  20771
USA

301-286-2040
William.T.Thompson at nasa.gov