Subject: Re: Identification of a FITS byte stream

From: [email-masked] (Archie Warnock)
Date: Fri, 3 Sep 93 15:44:45 -0400

So William Pence sez to me:
> COMMENT   A FITS (Flexible Image Transport System) format file as defined by 4
> COMMENT   Astronomy and Astrophysics Suppl. Series papers: v44, p363, v44, p371,
> COMMENT   v73, p359, and v73, p365.  The latest FITS definition document is
> COMMENT   available from the NASA/GSFC Office of Standards and Technology.

Looks fine to me - I think we can probably donate 320 bytes/file to
identify what the heck the format is, and the wording covers all the
bases. 

> I propose to add these comments immediately after the EXTEND keyword if
> it exists, otherwise immediately after the last NAXISn keyword.

The closer to the front of the file, the better, I think.  I'm all for
it!
_______________________________________________________________________
-- Archie Warnock              Internet:  [email-masked]
-- Hughes STX                  "Unix --- JCL For The 90s"
-- NASA/GSFC                   Project STELAR: WAIS to do science

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From: [email-masked] (William Pence)
Date: Fri, 3 Sep 93 14:31:24 -0400

Regarding Archie Warnock's suggestion of adding some identification
comments to FITS files, I drafted the following 4 lines which seem to
provide the essential information:

If and when we can agree on the wording, I will then modifiy the FITSIO
interface so that it automatically inserts these lines along with the
other required primary array keywords. 

-Bill Pence

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From: [email-masked] (Rob Seaman)
Date: Fri, 3 Sep 93 18:25:28 -0400

I like the suggestion for a "standard" block of comments to supply the
provenance of the FITS format.  This not only would provide a starting
point for the hypothetical astroarcheologists of the future, but may
also serve as a useful day-to-day reference for students and others
who find that they need to dig into the details of FITS.

However, I don't think the exact wording has converged yet.  Might I
suggest a slight revision:

COMMENT   FITS (Flexible Image Transport System) format, defined in Astronomy
COMMENT   and Astrophysics Supplement Series v44/p363 & v44/p371, extended
COMMENT   in v73/p359 & v73/p365.  Contact the NASA Office of Standards and
COMMENT   Technology for more recent FITS documents.

Note that the name of the journal is spelled out in full - the archeologists
may not speak English.  I would also suggest that the wording be as concise
as possible.  No need to fill up that final card.  While I'm sure this
version won't win the day either, I do think that the prose should be as
lucid as possible before it gets written into FITS headers the world over.

Is the "NASA/GSFC Office of Standards and Technology" the precise entity
that should be mentioned?  The User's Guide references the "NASA/Science
Office of Standards and Technology", while Barry Schlesinger is listed as
working for the "FITS Support Office" of the "NASA/OSSA Office of Standards
and Technology".  The NOST 100-1.0 standard lists "NASA/Science" on the
front cover, but then the "NASA/OSSA" variation is stamped at the bottom
of most of the pages.

Considering the nature of NASA it may well be that each of these "Offices
of Standards and Technology", "NASA/GSFC", "NASA/Science", and "NASA/OSSA"
have been the official name successively.  Will the comment block change
as NASA continues to change its internal structure?  (And what the heck
is the OSSA, anyway?)

It would be better to reference the standard itself rather than the
organization.  How about this variation?

COMMENT   FITS (Flexible Image Transport System) format, defined in Astronomy
COMMENT   and Astrophysics Supplement Series v44/p363 & v44/p371, extended in
COMMENT   v73/p359 & v73/p365.  The FITS standard is expressed in the NASA
COMMENT   Office of Standards and Technology document #100-1.0.

The comment block should be revised whenever the standard is revised.
The earlier references in preexisting FITS files will not be invalidated
since those files adher to previous versions of the standard.  All that
is required is that the standard be up-to-date for the current file.  A
less readable example of this is the first line of a PostScript file
which advertises compliance to a particular revision of PostScript.

Is referencing NASA the correct way to go at all?  (I politely suggest that
the "GSFC" be omitted in any case.)  The IAU "owns" the standard, not NASA.
Should the entire second sentence be removed until the IAU recognizes the
NOST standard?  (...and/or until the standard is printed in the refereed
literature?)  Is there any appropriate utilitarian reference to the IAU
that can be substituted?

One final suggestion that I believe was implicit in Bill and Archie's mail
is that this comment block only appear in a FITS file's primary header.

Rob Seaman
NOAO/IRAF
[email-masked]

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From: [email-masked] (Archie Warnock)
Date: Tue, 7 Sep 93 09:44:50 -0400

> COMMENT   Office of Standards and Technology document #100-1.0.

That's pretty good.

> literature?)  Is there any appropriate utilitarian reference to the IAU

I agree that there's no real reason to mention GSFC (except that right
now, that's where NOST is), but I think it would be a mistake to not
reference the NOST document for 2 reasons - it was put together by a
number of people in the community, not all affiliated with NASA (so it's
not just "NASA's document") and because it was intended to clarify some
ambiguous and contradictory points in the original FITS papers.  Now,
the original papers have benefits, too - namely accessibility in the
distant future, but I don't think that mentioning the NOST document is
inappropriate in the scheme of documenting what FITS is to the reader.

> is that this comment block only appear in a FITS file's primary header.

Sure - no sense beating this to death...

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From: "BARRY M. SCHLESINGER" <[email-masked]>
Date: Wed, 8 Sep 93 09:34:10 -0400

From:	SMTP%"[email-masked]"  3-SEP-1993 18:42:04.74
To:	BSCHLESINGER
CC:	
Subj:	Re: Identification of a FITS byte stream

> front cover, but then the "NASA/OSSA" variation is stamped at the bottom

That must have been soon after the standard was posted.  All the pages
should say NASA/Science now. 

> as NASA continues to change its internal structure?  (And what the heck

OSSA was the Office of Space Science and Applications, since 
reorganized out of existence.  The NASA/Science name is the third 
since 1989.  Future name changes, as the visions of management and the 
overlying organization change, are not out of the question.

> ... How about this variation?

> is required is that the standard be up-to-date for the current 
> file.... 

By the "once FITS, always FITS" rule in the Generalized Extensions 
paper, if a file was conformant to the FITS standard at an earlier
time, it will still be conformant as extensions are made to FITS; no
change may be made that will make the file non conformant.

> literature?)  Is there any appropriate utilitarian reference to the IAU

The IAU General Assembly has formally endorsed the four FITS papers
and Floating Point agreement as the standard for FITS.  The NOST
document was developed to resolve ambiguities and contradictions in
the original papers. It is now being considered for endorsement by the
IAU FITS Working Group; if approved, a resolution would be submitted 
to the 1994 General Assembly.  

The name of the office is the NASA/Science Office of Standards and
Technology; GSFC is not part of the name and should be omitted. As for
the role of the NOST, one might look at how the FITS extension
registry works, where NOST serves as an agent of the IAU FITS
Working Group in the process of registering FITS extension type names.

				Barry Schlesinger
				NOST FITS Support Office

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From: [email-masked] (William Pence)
Date: Thu, 9 Sep 93 14:02:13 -0400

> COMMENT   Technology for more recent FITS documents.

To interate on this a little further, and including Barry Schlesinger's
comment on the correct title for the NOST, I'd suggest the following version:

COMMENT   FITS (Flexible Image Transport System) format defined in Astronomy and
COMMENT   Astrophysics Supplement Series v44/p363, v44/p371, v73/p359, v73/p365.
COMMENT   Contact the NASA Science Office of Standards and Technology for the
COMMENT   FITS Definition document #100-1.0 and the FITS User's Guide.

This compresses the information in the first sentence to make room for
the reference to the NOST Definition document and User's Guide on the 4th line.

-Bill Pence