[postgis-devel] Hi About postgis extensions
strk at refractions.net
strk at refractions.net
Fri Mar 2 03:19:01 PST 2007
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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