geometry poligons performance and index

From: giuseppe(dot)derossi(at)email(dot)it
To: pgsql-admin(at)postgresql(dot)org
Subject: geometry poligons performance and index
Date: 2007-08-29 06:54:45
Message-ID: 77edfa82157a698e4c207fcdaccc52f2@164.129.1.43
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Hi
I need to set a query which performs a intersection check between two set
of
polygons which are stored into two tables.
I wrote the where instruction so:
...
where area(intersection(t1.the_geom,t2.the_geom))>0
...

The results are ok, but the query is too slow. I tried to applay a GIST and
gtree index but performance did not improve.
By explaining the query I see that the where condition gets the query slow.
Is there a more simple way to check if two poligons have a not null
intersection (they overlap)?

Is there a kind of index I can use ?

THanks

Giu

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