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List:       postgis-devel
Subject:    Re: [postgis-devel] Hi About postgis extensions
From:       strk () refractions ! net
Date:       2007-03-02 11:19:01
Message-ID: 20070302111901.GU42595 () keybit ! net
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On Thu, Mar 01, 2007 at 11:29:54PM -0600, Chengyang wrote:
> Hi,
> I am planning to develop a extension for GROUP BY in postgis.
> Could anyone tell me where to start from?
> I can barely find any document on PostGIS development.
> I am good at java. Is there anyway to work with Java to do this?

GROUP BY, togheter with DISTINCT rely on theequality operator
from the btree index. Postgis provides a btree index for specifically
this support. To make things fast the equality only uses bounding
box comparison. If you want to test for vertex-by-vertex equality or topological
equality things would be much slower, and for topological equality the GEOS 
library would be an additional requirement.

--strk;
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