[fitsbits] The CONTINUE and HIERARCH Conventions Public Comment Periods

[Rob Seaman]

If the registry serves to bring order to chaos, it will be a net  
positive.  If it serves, rather, to advertise conventions willy- 
nilly, it may be a net negative.  I'm really nervous at the thought  
of random naive users including HIERARCH keywords in their  
documents.  Bob's examples and Bill's comments demonstrate that even  
expert FITS users may differ on the legality of HIERARCH usage.

On Sep 10, 2007, at 9:45 AM, William Pence wrote:

> I initially shared your dislike of the HIERARCH convention, but have
> changed my mind after seeing how well it has worked in the ESO FITS
> files.  If you look at the sample FITS header listing from ESO  [...]
> there are hundreds of keywords that use this convention in each file.

One has always wondered at the project requirements that lead to  
including hundreds of keywords in a FITS file.

> I agree however that it probably would not make sense to use the  
> HIERARCH
> convention for just a couple keywords in a file.

Can we hope to successfully legislate this?

> I don't particularly like the more generalized use of the HIERARCH
> convention to create keyword names that are longer than 8  
> characters or
> contain non-standard characters (even though I added support for  
> this in
> the CFITSIO library).

Me neither!

> If we really want to extend FITS to allow longer
> keyword names, then I think a much simpler way to do this is to just
> allow free-format keyword records in which the "=" can appear anywhere
> after byte 9 of the record, such as:
>
> MY_LONG_KEYWORD = 17 / comment string

Bleh!  No, no, no.  Talk about needing to version FITS...

> Note that this keyword is perfectly legal under the current FITS
> Standard: existing FITS readers should interpret this as a
> commentary-type keyword, with the 8-character name "MY_LONG_"
> and the rest of the record treated as a comment string.

I don't think we've ever tested this in anger.  A lot of FITS  
applications likely still assume that the only commentary keywords  
are COMMENT, HISTORY and <BLANK>.  We just had an issue with a  
technically legal <BLANK> keyword throwing an error due to an  
extraneous equals sign in column nine.

If we want to address the issue of including elaborate header  
metadata in FITS, I suspect I wouldn't be alone in preferring a  
bintable based solution, perhaps located as the last HDU at the end  
of each file (where lots of folks wanted the header in the first  
place).  This, too, is already perfectly legal FITS.

Rob