[postgis-devel] Lame attempt at cascade union in sql

Obe, Regina robe.dnd at cityofboston.gov
Fri Aug 8 08:56:29 PDT 2008


Yap Kevin gave me his sample dataset and that's what I've been using to
compare his results with mine. What is the processor on your box?  I
gather Kevin and I must be running something similar since our timings
seem about the same.

-----Original Message-----
From: postgis-devel-bounces at postgis.refractions.net
[mailto:postgis-devel-bounces at postgis.refractions.net] On Behalf Of
Martin Davis
Sent: Friday, August 08, 2008 11:52 AM
To: PostGIS Development Discussion
Subject: Re: [postgis-devel] Lame attempt at cascade union in sql

Regina, I'm not sure what I can really test for you - I don't have 
PostGIS on my box, so it's difficult to replicate these tests.  And 
subsetting the geometries in JTS isn't going to give the same result 
set, due to the clustering.  Or am I missing something?  Is your sample 
dataset the same one that Kevin & I are using?

Anyway, don't feel too bad - I think there's a fundamental performance 
difference between the basic union function in JTS and in GEOS.  Java is

much more efficient at memory allocation than C++ is (at least, using 
std C++ memory operations).  So barring a stroke of genius in GEOS-land 
I think JTS is alway going to out-perform.

Also, despite my earlier sarcastic remark about processor speed, this 
*is* going to make a difference - perhaps by 2-3x?  (Although I don't 
have a screaming fast box by any means...)

M
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