more on FITS and VO

[Mike Fitzpatrick]

Jonathan McDowell <jcm at head.cfa.harvard.edu> wrote:

> Because there are plenty of multi-extension files consisting of an image
> and further extensions which are not essential for interpretation of that
> image. (As one example, we have X-ray spectra which store an image of the
> extraction region in the primary array. You don't need to care that the
> file has a spectrum in order to do something with the image of the
> extraction region).

	Fair enough.  I suspect services with such data would make
smart choices about when the overhead of sending the extra bytes exceeds
the cost of stripping out the primary data, but in cases where they don't
wouldn't I still have to know something about where in that file the
data I'm actually interested in lies?  What if the spetrum were the
primary data and I wanted the extraction region in the extension?  Such an
image is still valid image/fits, and while forcing the consumer to understand
my storage scheme may mean I don't end up w/ a popular service, as somebody 
writing software to understand the mime type I need to worry about it
such abuses.

> Now in the NOAO approach of (if I understand correctly) representing
> mosaic images as one chip in the primary array and a bunch more in image
> extensions, doing this would be unhelpful to the user and you would probably
> not choose to represent them as image/fits.

	Not that it matters much here, but all of the images are stored 
in extensions, there is no primary array in an NOAO Mosaic MEF (unless
I MUST add the pixel...)

Cheers,
-Mike