more on FITS and VO

[William Pence]

The intent of this subtle change is wording is to allow the "image/fits"
mimetype to be legally applied to FITS files in which the Primary
array has NAXIS greater than zero, and has one or more NAXISn keywords
equal to zero, and thus contains 0 pixels,  e.g.,
  NAXIS  =   2
  NAXIS1 = 100
  NAXIS2 =   0

Take for example a web site or service that returns 2-dimensional FITS
images to the browser, with mimetype 'image/fits'.   Some people have
argued that there could be times when the web site would need to return
a zero pixel length image, e.g., the user might only want the FITS
header information (metadata) without the image itself, or a zero pixel
image might be returned if the requested image position was not available
for some reason (outside of the area covered by a survey).  For whatever
reason, some people have argued, there *might* be occasions where the 
web service would need to return a zero pixel image, and in that case
it would be more convenient, and less confusing to the end user, to assign
'image/fits' to the file, just like all the other images that it returns.

These examples are perhaps a bit contrived, but the advocates for this
change in wording argue that it would be better to not forbid this
use of 'image/fits' because more compelling uses for it may arise
in the future.

Note that it was not intended that this be applied to the Random Groups FITS
files (which by convention have NAXIS1 = 0) because Random Groups
are rarely used to store a single 'image'.  It would be more
appropriate to classify most Random Groups files as 'application/fits'.

-Bill Pence   

On Thu, Nov 27, 2003 at 10:51:36AM -0500, Patrick P Murphy wrote:
> On Thu, 27 Nov 2003 12:29:38 +0000 (GMT), Guy Rixon <gtr at ast.cam.ac.uk>
>    said: 
> 
> > On Wed, 26 Nov 2003, Robert Hanisch wrote:
> 
> >> I've been asked to poll the VO community concerning the proposed FITS MIME
> >> type and a restriction that has been suggested:
> 
> (quoting from Bill Pence):
> 
> >>> Do you, or other members of the VO community, have any objections to
> >>> this change to the FITSMIME proposal?  The effect of this one word
> >>> change (from 'must' to 'should') would be to allow null images (with
> >>> one or more NAXISn keywords = 0) to be given the mime type
> 
> Note: NAXIS**n**, i.e. NAXIS1 or NAXIS2 etc.  
> 
> >>> "image/fits".  Without this change in wording this would not be
> >>> allowed, and such null images would have to be given the mimetype
> >>> "application/fits".  This appears to be the last question to be
> >>> resolved before the FITS committees can vote on the proposal (very
> >>> soon I hope).
> 
> > This change sounds unhelpful.  Something with NAXIS=0 isn't an image; 
> 
> While it's a semantic point, what the proposal said did not refer to the
> NAXIS (number of axes) keyword, but to the value of one or more of the
> NAXIS1, NAXIS2, etc. keywords being zero.  This feature is most often
> used by the non-optical Astronomy community (Radio, X-ray, etc).
> 
> > you can't display it in an image viewer.  Surely the point of
> > image/fits is to separate those datasets that can be passed to a
> > generic image-viewer from those where the receiving programme needs to
> > know the semantics of the data?
> 
> Point taken, but what should we then do about our UV-DATA and other
> files that qualify as valid FITS files but have NAXIS1=0; are they to be
> excluded from using the image/fits MIME type?
> 
> 				- Pat
> -- 
>  Patrick P. Murphy, Ph.D.           Division Head, CV Computing, NRAO
>  Home: http://goof.com/~pmurphy/    Work: http://www.nrao.edu/~pmurphy/
>  "Laws of nature are...just parochial by-laws in our cosmic patch"
>                                                     - Martin Rees