REGION

[Francois Ochsenbein]

Hi,

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....
--francois

>
>Hi there,
>
>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:
> http://www.pha.jhu.edu/~gyuri/htm/HtmPrimer/regiongrammar.html
>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.
>Inaki
>

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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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