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

[Seaman, Robert Lewis - (rseaman)]

Hi Gregory,

As folks can infer from my ancient comments, I’m leery of relying on such fiddly features, and I also had nothing to do with whatever wording of either CONTINUE or “type long-string” in the FITS standard.

What I’m wondering is whether Rubin or SPHEREx are really using CONTINUE – specifically, that is, with mandatory or reserved keywords. What is the use case?

Or are you rather wondering if you need to support type long-string in general? Note that it is perfectly legal FITS to define a bintable extension to contain all metadata that in antediluvian days would have shown up in ASCII header keywords. One can leave the structural FITS headers for the mandatory keywords and a short list of others like CHECKSUM and avoid using awkward conventions or data types entirely.

That said, if you are worrying about writing documentation explaining your FITS usage, Rubin software and data must be quite mature at this point.

Rob



On 2/25/25, 12:04 AM, "fitsbits" wrote:

External Email

Dear colleagues,

FITS 4.00, §4.2.1.2<http://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<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 Or was it intended to actually be used for some particular keyword(s) in the standard, but with that intent withdrawn before 4.00 actually appeared?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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