[postgis-devel] CascadedUnion Early Results
Paul Ramsey
pramsey at cleverelephant.ca
Tue Jan 20 15:10:43 PST 2009
This test case is taking a *very* long time for the standard function.
No answer yet :)
P
On Tue, Jan 20, 2009 at 2:29 PM, Kevin Neufeld <kneufeld at refractions.net> wrote:
> Yup, already forwarded it to you.
>
> Yes, it looks much better. It obviously depends greatly on the dataset
> being used ... just how much the dataset overlaps.
>
> Paul, out of curiosity, how does this method compare when trying to use a
> set of completely disjoint polygons? Since there is nothing to gain by
> using a cascaded methodology in such a case, is there an overhead to using
> the function?
>
> Cheers,
> Kevin
>
> Obe, Regina wrote:
>>
>> Ah okay that looks good. I think the numbers look like about what I got
>> on JTS.
>>
>> I have to dig up that set Kevin had given me way back when. Kevin you
>> don't still happen to have that do you? I think it was named
>> sample_poly.zip
>>
>>
>>
>> -----Original Message-----
>> From: postgis-devel-bounces at postgis.refractions.net on behalf of Paul
>> Ramsey
>> Sent: Tue 1/20/2009 5:08 PM
>> To: PostGIS Development Discussion
>> Subject: Re: [postgis-devel] CascadedUnion Early Results
>>
>> Here's your test, slightly modified. Shows about 30-times improvement
>> over traditional union.
>>
>> SELECT state,
>> SUM(ST_NPoints(the_geom)) As numpointsbefore,
>> ST_NPoints(ST_Union(the_geom)) As numpointsafter
>> FROM usstatebounds
>> GROUP BY state
>> ORDER BY state;
>>
>> Time: 579121.791 ms
>>
>> SELECT state,
>> SUM(ST_NPoints(the_geom)) As numpointsbefore,
>> ST_NPoints(ST_Union_Fast(the_geom)) As numpointsafter
>> FROM usstatebounds
>> GROUP BY state
>> ORDER BY state;
>>
>> Time: 21145.717 ms
>>
>>
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