[geos-devel] Nightly build performance

[James.Sewell at lisasoft.com]

Greetings GEOS Devs,

I have been trying the GEOS and POSTGIS from a nightly build to test ST_Snap. I am still trying it out but have come across another issue.

I am currently running the following:

	POSTGIS="2.0.0SVN" GEOS="3.3.0-CAPI-1.7.0" PROJ="Rel. 4.7.1, 23 September 2009" LIBXML="2.6.26" USE_STATS

And comparing performance to:

	POSTGIS="1.5.2" GEOS="3.3.0-CAPI-1.7.0" PROJ="Rel. 4.7.1, 23 September 2009" LIBXML="2.6.26" USE_STATS

(The first GEOS is actually nightly while the second isn't - yet they report the same version)

The issue I have noticed is that the newer version is noticeably (more than 5x) slower on some large queries of the form:

	SELECT a.geom FROM left AS a, right AS b    
		WHERE st_intersects(a.the_geom, b.the_geom);


Have there been changes in this area of the code? Is this expected for nightly builds? Is there anything I can do to help troubleshooting of the issue? All my tables are imported and indexed by the same tool in both instances.

Cheers,
James Sewell 
Developer 
LISAsoft 

Ph: +61 3 8680 3250 Fax: +61 3 8680 3299 
Level 9, 601 Bourke St, Melbourne Vic 3000


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-----Original Message-----
From: geos-devel-bounces at lists.osgeo.org [mailto:geos-devel-bounces at lists.osgeo.org] On Behalf Of strk
Sent: Thursday, 3 February 2011 7:14 PM
To: GEOS Development List
Cc: jts-topo-suite-user at lists.sourceforge.net
Subject: Re: [geos-devel] RE: [Jts-topo-suite-user] JTS Topology error

On Thu, Feb 03, 2011 at 10:25:08AM +1030, James.Sewell at lisasoft.com wrote:
> (Crossposting to GEOS list)
> 
> I see. So the difference between the GeometryNoder with a PrecisionModel and using ST_Snaptogrid from PostGIS on the input geometries is that the GeometryNoder snaps all nodes which are created by the noding process as it works?
> 
> This seems like an elegant solution to deal with the roundoff issues.
> 
> I gather GEOS doesn't expose noding functionality in this way? Is this something that could possibly be added? From PostGIS would a command like ST_Node(geometry, 10E-10) make sense / be plausible? Or would a better solution be to define the precision for each geometry column?

Check the new ST_Snap() function in PostGIS and GEOS svn repository.

--strk;

  ()   Free GIS & Flash consultant/developer
  /\   http://strk.keybit.net/services.html
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