[fitsbits] Keywords "explicitly declared ... long-string"? {External} {External}

[Francois-Xavier PINEAU]

Dear Gregory,

While I don't have the exact answer, we can pool our best guesses.
So, here how I understand it.

In "The Philosophy of FITS", here
   https://fits.gsfc.nasa.gov/users_guide/users_guide/node7.html
, we find:
"As far as is possible, however, FITS should be expanded in such a way that
the old software will still be able to process those parts of the file 
which
it is capable of handling. In such a case, software should not fail or give
incorrect results when confronted with the new extension or conventions;
it should simply ignore them and continue to process those parts of the file
that it can understand."

Thus, I tend to think that the sentence you quoted:
   "The CONTINUE keyword must not be used with of [sic] any of the 
mandatory or
   reserved keywords defined in this Standard unless explicitly declared 
of type long-string."
simply leaves doors opens to the future while ensuring the compatibility
of unmaintained software with keywords that were already defined 
(mandatory + reserved)
in the previous versions of the FITS standard.

Returning truncated values (with a final '&') for string keywords
describing observations (such as 'TELESCOP') or bibliographic keywords
('AUTHOR', 'REFERENC') does not seems to be harmful (so one may have 
expected
those to be defined as 'long-string' in FITS4.0).
But the example of CHECKSUM here (by Rob Seaman)
https://fits.gsfc.nasa.gov/registry/continue/continue_fitsbits_mail.txt
probably leads to a certain conservatism.
In the link, you will also find the following explicit demand by Craig 
Markwardt:
   "Bill, could the convention be clarified to indicate that CONTINUE
   should not be used for keyword values that could fit in a single FITS
   card?  And/or, that CONTINUE should be avoided for standard FITS
   keywords?"
Even if one also finds (at the end, by William Pence):
   "As currently defined, the record-valued keywords all have string values,
   so there shouldn't be any problem with using this continuation
   convention with them, if desired"

I would thus say both 1 and 2, and not 3 (but I may be contradicted by
more informed people and/or differing opinions).

Best regards,

F.-X. Pineau

Le 25/02/2025 à 07:47, Dubois-Felsmann, Gregory P. via fitsbits a écrit :
> Dear colleagues,
>
> FITS 4.00, §4.2.1.2 "Continued string (long-string) keywords" contains the statement:
>
> "The CONTINUE keyword must not be used with of [sic] any of the mandatory or reserved keywords defined in this Standard unless explicitly declared of type long-string."
>
> I have looked moderately diligently through the whole of FITS 4..00 as well as https://heasarc.gsfc.nasa.gov/docs/fcg/standard_dict.html and I cannot find an instance of a keyword "declared of type long-string".
>
> Was this sentence included as groundwork for the possible future introduction of keywords declared as long-string?  Or to support projects that wish to declare keywords of their own as long-string?  Or was it intended to actually be used for some particular keyword(s) in the standard, but with that intent withdrawn before 4.00 actually appeared?
>
> This is not a theoretical question; we are working on polishing our standards-compliance in both Rubin and SPHEREx prior to the release of data to users later this year.
>
> Many thanks,
> Gregory
>
> --
> Gregory Dubois-Felsmann, Ph.D. | Senior Staff Scientist | Caltech/IPAC
> Science Platform Scientist, Vera C. Rubin Observatory
> Pipeline System Designer, NASA SPHEREx mission
> Mail Code MR 100-22 | Pasadena, CA 91125-2200 | gpdf at ipac.caltech.edu
>
>
>
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