[postgis-devel] CascadedUnion Early Results

[Kevin Neufeld]

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
> 
>