francois at vizir.u-strasbg.fr
Wed May 9 10:15:01 PDT 2007
Sorry, but the Region construct on the quoted page is a formal
definition on how a REGION is written -- it clarifies the vocabulary
and the syntax, but it is not defined as a function neither it specifies
how it's written and combined with other predicates in a query.
Or did I overlook ?
For circular regions, Alex's examples use a function
fDistanceLonLat(lon1, lat1, lon2, lat2)
which returns the spherical distance between 2 points which
can be table columns or actual numbers. If the 2 sets of positions
are in the same frame, there is no need to specify the actual frame --
just the four numbers are necessary and sufficient for this purpose.
This function is therefore the only thing which is required to define /
compute / select on the basis of any combination of circular regions.
Making the selection efficient is completely different question.
See you soon for lively discussions....
>Alex suggested us to have a look at the NVO Footprint Service to check
>whether it can be of use within the ADQL. As he is traveling today and
>might not be able to start the discussion, I will comment it here,
>pointing to the relevant pages.
>In our opinion all that we need to specify a region, not the full
>predicate construct, is already there. From the main pages of the
>Footprint Service (announced last November,
>http://www.voservices.net/footprint/), you can access a link to a very
>simple and useful grammar definition that we could use:
>This looks to us as a clean and reasonable approach. So please disregard
>my previous suggestion of contacting Arnold Rots for clarification on an
>eventual STC-like string serialization. Fortunately, everything is
>already there :-)
>Please tell us what you think.
Francois Ochsenbein ------ Observatoire Astronomique de Strasbourg
11, rue de l'Universite F-67000 STRASBOURG Phone: +33-(0)390 24 24 29
Email: francois at astro.u-strasbg.fr (France) Fax: +33-(0)390 24 24 17
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