[geos-devel] [GEOS] #343: After applying a buffer over a multiline the library starts growing in memory usage and hungs

[Martin Davis]

I'm surprise that PostGIS is so much faster too!  Can you supply the 
output, so I can check it against JTS?

One thing I notice is that the input I'm using has 5615 elements and 
11502 points.

This *might* make a big difference, if you are missing some of the 
bigger linestrings which (a) have large buffer polygons and (b) 
intersect *all* of the other elements' buffers.

strk wrote:
> On Thu, May 13, 2010 at 09:22:49AM -0700, Martin Davis wrote:
>   
>> Just tried the buffer-and-union approach in JTS.  It works fine - about 
>> 70 s for the union, less for the initial buffering.  Memory usage was low.
>>     
>
> I tried buffer-and-union approach in PostGIS.
> It was very fast !
>
> Some stats:
>
>  - Original geometry is a MULTILINESTRING with 3272 components
>  - Average number of points per component: 3.3 (from 2 to 93)
>  - Total number of points: 10677
>
> Postgis operations with timing:
>
>  $ time psql -c 'create table bug_dump2 as select (st_dump(g)).* from bug;'
>  real    0m0.330s
>  user    0m0.032s
>  sys     0m0.012s
>
>  $ time psql strk -c 'update bug_dump2 set geom = st_buffer(geom, 0.005)';
>  UPDATE 3272
>  real    0m0.463s
>  user    0m0.040s
>  sys     0m0.008s
>
>  $ time psql strk -Ac 'select st_npoints(st_union(geom)) from bug_dump2';
>  st_npoints: 1336
>  real    0m1.181s
>  user    0m0.040s
>  sys     0m0.008s
>
> This is postgis trunk (to be 2.0.0) with GEOS trunk (to be 3.3.0).
>
> I'm surprised it takes 70 seconds with JTS. Am I doing anything wrong here ?
>
> --strk;
>
>   ()   Free GIS & Flash consultant/developer
>   /\   http://strk.keybit.net/services.html
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>   

-- 
Martin Davis
Senior Technical Architect
Refractions Research, Inc.
(250) 383-3022