REGION

[Iñaki Ortiz de Landaluce]

Hi Francois

I think that we might be talking about two different things here. I see 
your use-case more related with the usage of a specific User Defined 
Function (fDistanceLonLat) rather than the REGION predicate itself. In 
my opinion, computing and comparing the distances among tuples of points 
with overlapping errors goes beyond the initial idea of computing the 
action of an operator/verb (INTERSECTS, CONTAINS, DISJOINT ...etc) over 
a region specification. I think that these kind of  requirements could 
be easily handled by the standard function placeholder in the following 
way (or similarly):

 WHERE [... AND] fDistanceLonLat(t1.lon, t1.lat, t2.lon, t2.lat) < 
(t1.pos_err + t2.pos.err)

Cheers
Inaki


Francois Ochsenbein wrote:
> Hi Inaki,
>
> OK, it's therefore just for the region syntax (not the query), sorry
> for the misunderstanding. 
>
> But I still don't see how you would write with regions how, for instance,
> you would write a search for tuples with overlapping error ellipses.
> I mean assuming 2 tables having the same schema (lon, lat, lon_err, lat_err)
> you could with the REGION syntax write the condition to get the
> tuples with overlapping regions ? 
>
> For circles (i.e. assuming that lon_err is always identical to lat_err 
> on both tables, and I call them just "pos_err"), the predicate
>
>     fDistanceLonLat(t1.lon, t1.lat, t2.lon, t2.lat) < (t1.pos_err + t2.pos_err)
>
> locates all tuples with overlapping error circles. How would you write
> this condition with the REGION syntax ? 
>
> Cheers, francois
>
>   
>> Hi Francois
>> What I was proposing was to use the BNF I was describing in the email
>> before, which I believe is consistent with what Alex was suggesting,
>> plus the specific syntax of the REGION following the specification of
>> the footprint service. Therefore my suggestion would be like this:
>>
>> <predicate> ::= <comparison_predicate>| <between_predicate> |
>> <in_predicate> | <like_predicate> | <null_predicate>
>> | <exists_predicate> | <region_predicate>
>>
>> <region_predicate> ::=
>> REGION<period><region_verbs>
>> <left_paren>
>> <region_specification>
>> [ <comma> <column_reference> [ { <comma> <column_reference> }... ] ]
>> <right_paren>
>>
>> <region_verbs> ::= INTERSECTS | CONTAINS ...
>> <region_specification>
>> ::= !! 'Footprint Service'-like syntax, e.g. RECT LATLON 37 -109.55  41 -102.05
>>
>>
>>     
>
> ================================================================================
> 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 32
> ================================================================================
>   

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