[fitsmime] Thoughts on FITS MIME types.

[Steve Allen]

On Mon 2002-12-09T20:28:12 -0500, Tom McGlynn hath writ:
> the Image/FITS specification makes sense for FITS files with no extentions
> and with a 2-dimensional image.  These correspond to the notions of the
> other image data sets and this very basic notion of FITS  has been used
> outside
> of the standard suites of astronomical software (e.g., in versions of
> the XV program).

The image/* MIME types for AutoCAD encode 3-d vector information as
well as constructive solid geometry (CSG) models (e.g., if we take
these two 2-d shapes, revolve them around their respective axes to
make solids of revolution, and then pivot the results around that
axis, would the resulting pieces of metal collide with each other?).
These AutoCAD formats are much more nearly congruent with the MIME
"model" type than it is with the MIME "image" type.

It is for this reason that I do not believe that image/fits need be
restricted to 2-d images.  Even if it were to be restricted to 2-d, I
believe that WCS table extensions must be legally admitted, for to do
less is to ignore the existence of elements of FITS which are about to
receive the accord of full standard.


Nevertheless, even with recent support from Don Wells for
"application/fits-groups" I remain skeptical about anything other than
"application/fits" because of the precedent set by
"application/postscript".  PostScript has had three different
incarnations (original, Level 2, and Level 3), yet there is only one
MIME type for PostScript.  It is up to the receiving application to
ascertain whether it can handle the incoming PostScript code.

Hopefully the PostScript code contains comments which indicate whether
it is level 3 or level 2.  Ideally it also contains code for
conditional procedures which check the version level of the
interpreter and invoke verbose workaround procedures that enable
an old interpreter to handle new features.  But neither of these is
required.  In their absence, an old interpreter invoked because of
the MIME type "application/postscript" will simply fail.

FITS is already in much better condition than this, for there is no
valid FITS file which should cause HEASARC's fv and similar
applications to fail.


I am hoping to see some input from the VO community here, but at
present my impression remains that the RFC should register
	image/fits
	application/fits
and that the rest of the issues raised here are best solved by
starting up classification efforts within the FITS community.

--
Steve Allen          UCO/Lick Observatory       Santa Cruz, CA 95064
sla at ucolick.org      Voice: +1 831 459 3046     http://www.ucolick.org/~sla
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