gzipped images in SIAP 1.0 (fwd)

[Patrick Dowler]

On Wednesday 30 May 2007 14:59, Doug Tody wrote:
> The first question asked was what SIAP 1.0 intended, and this is what
> I have addressed above.  SIAP has always worked this way, and I am
> surprised that anyone is confused.

I don't think the FORMAT thing in SIA 1.0 is confusing. For most people, I 
expect, the collection they are serving is in one format or they decide to 
serve one format, so if a query comes in asking for GIF and they only have 
FITS, they return an empty VOTable (this is what we do). 

We have also toyed with on-the-fly conversion, which if deployed would mean we 
could respond "yes" to any format and do the conversion in the getData stage. 
This and the above approach are both kind of "a priori" knowledge of the 
possible types, without doing a DB query.

We also have in some cases pre-computed preview images in graphics format, but 
I always found it kind of ugly for the observation catalog to know about 
these different formats. Essentially, trying to support this in a really 
general way brings in a very large database denormalisation problem, 
especially when you have set of systems for storing all the files and another 
for enabling the querying of metadata. I prefer to leave the file type stuff 
for the delivery mechanism to handle (eg the getData method) since that can 
be largely independent of the querying (except in this case of formats).

if one had the on-the-fly conversion in place, then pre-computed previews (for 
example) could be just an optimisation of the retrieval process, which is 
again nice and clean and simple. But in general I think this FORMAT thing is 
an optimisation that introduces some complexity to implementing the service 
in some cases. It is easy enough to avoid that by reducing the scope of the 
service (eg we have fits and jpg but only deliver fits because we don't 
always have jpg on hand) but that does reduce overall value.

summary: it's more complicated than it looks, but not confusing :-)

-- 

Patrick Dowler
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