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<TITLE>RE: [postgis-devel] Lame attempt at cascade union in sql</TITLE>
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<P><FONT SIZE=2>I think its C++. But I still have a couple of tricks up my sleeve. Anyrate eventually you are right it should be<BR>
in GEOS. Just don't have the c++ skills to port JTS to GEOS yet. So this is just a stopgap measure. As a side note- a completely pure<BR>
PostgreSQL solution would mean people don't need to upgrade to the latest GEOS to get the benefits.<BR>
<BR>
-----Original Message-----<BR>
From: postgis-devel-bounces@postgis.refractions.net on behalf of Kevin Neufeld<BR>
Sent: Fri 8/8/2008 1:22 AM<BR>
To: PostGIS Development Discussion<BR>
Subject: Re: [postgis-devel] Lame attempt at cascade union in sql<BR>
<BR>
Hmmm. Still, I give you an applause for the speed an simplicity of your<BR>
attempt. Even my crazy looking GROUPBY/ORDERBY query that runs in 1min<BR>
is still 3 times slower than Martin Davis's Java code in JTS. Ideally,<BR>
it would be best for someone to put the thing through GEOS so PostGIS<BR>
can benefit from it as well. Anyone feel like brushing up on their C? :)<BR>
<BR>
-- Kevin<BR>
<BR>
Obe, Regina wrote:<BR>
><BR>
> Curiosity got the better of me this time so I ran thru the full set<BR>
> once and got this. So still better, but I guess there is still room<BR>
> for improvement and my cascading seems to not be growing linearly as<BR>
> Kevin's is.<BR>
><BR>
> --277,656 ms = 4.6276 minutes<BR>
> SELECT ST_CascadeUnion(the_geom)<BR>
> FROM (SELECT * FROM sample_poly) As foo;<BR>
><BR>
> --69,953 ms = 1.16 minutes<BR>
> SELECT ST_Union(the_geom) AS the_geom<BR>
> FROM (<BR>
> SELECT min(id) AS id, ST_Union(the_geom) AS the_geom<BR>
> FROM (<BR>
> SELECT min(id) AS id, ST_Union(the_geom) AS the_geom<BR>
> FROM (<BR>
> SELECT min(id) AS id, ST_Union(the_geom) AS the_geom<BR>
> FROM (<BR>
> SELECT min(id) AS id, ST_Union(the_geom) AS the_geom<BR>
> FROM (SELECT * FROM sample_poly) As foo<BR>
> GROUP BY round(id/10)<BR>
> ORDER BY id) AS tmp1<BR>
> GROUP BY round(id/100)<BR>
> ORDER BY id) AS tmp2<BR>
> GROUP BY round(id/1000)<BR>
> ORDER BY id) AS tmp3<BR>
> GROUP BY round(id/10000)<BR>
> ORDER BY id) AS tmp4<BR>
> GROUP BY round(id/100000);<BR>
><BR>
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