Thanks Martin, I'll install the latest nightly build of GEOS, recompile PostGIS and hope for the best.
Reading the thread does that mean that st_union(geom, geom) should work in this case? I had previously done some testing and it didn't seem to, I'll test again though. Cheers, James Sewell Developer LISAsoft ________________________________ Ph: +61 3 8680 3250 Fax: +61 3 8680 3299 Level 9, 601 Bourke St, Melbourne Vic 3000 ________________________________ LISAsoft is part of the A2end Group of Companies http://www.ardec.com.au<http://www.ardec.com.au/> http://www.lisasoft.com<http://www.lisasoft.com/> http://www.terrapages.com<http://www.terrapages.com/> From: geos-devel-boun...@lists.osgeo.org [mailto:geos-devel-boun...@lists.osgeo.org] On Behalf Of Martin Davis Sent: Friday, 14 January 2011 2:51 PM To: geos-devel@lists.osgeo.org Subject: Re: [geos-devel] RE: GEOS errors from PostGIS James, I suspect this may be caused by a known bug in the Unary union. This was identified in this thread on the JTS list: http://sourceforge.net/mailarchive/forum.php?thread_name=4C0FB4A5.2010304%40refractions.net&forum_name=jts-topo-suite-user I fixed this in JTS, in the soon-to-be-released ver 1.12. Perhaps this fix hasn't made it's way into GEOS and PostGIS yet. The thing to do is to get this fixed in GEOS, rolled into PostGIS, and then you can retest your union case. Martin On 1/11/2011 6:23 PM, james.sew...@lisasoft.com<mailto:james.sew...@lisasoft.com> wrote: Sorry, I didn't include the actual error: An example is: NOTICE: TopologyException: found non-noded intersection between LINESTRING (143.861 -36.881, 143.861 -36.881) and LINESTRING (143.861 -36.881, 143.861 -36.881) at 143.861 -36.881 This particular one is a two very small identical lines, this isn't always the case but seems to be the majority of the time. Cheers, James Sewell Developer LISAsoft ________________________________ Ph: +61 3 8680 3250 Fax: +61 3 8680 3299 Level 9, 601 Bourke St, Melbourne Vic 3000 ________________________________ LISAsoft is part of the A2end Group of Companies http://www.ardec.com.au<http://www.ardec.com.au/> http://www.lisasoft.com<http://www.lisasoft.com/> http://www.terrapages.com<http://www.terrapages.com/> From: james.sew...@lisasoft.com<mailto:james.sew...@lisasoft.com> Sent: Wednesday, 12 January 2011 12:06 PM To: 'geos-devel@lists.osgeo.org<mailto:geos-devel@lists.osgeo.org>' Subject: GEOS errors from PostGIS Hello All, I am currently creating an OSS Python app which uses PostGIS (and thus GEOS) to combines multiple layers and carries through attributes. I am using a method derived from Paul Ramsey's http://s3.opengeo.org/postgis-power.pdf document. The steps I am taking are as follows: Take the left and right layers and split them into smaller segments Iterate through the segments doing the following: Use the following to dump each side to linework SELECT ST_Collect(a.the_geom) AS the_geom FROM (SELECT (ST_Dump (ST_Exteriorring( (ST_Dumprings( (ST_Dump(the_geom)).geom)).geom))).geom AS the_geom Put two resulting multi-polygons into a table, make sure they are valid (and all encapsulated polys are valid), and union to remove overlap as follows SELECT ST_Union(ST_snaptogrid(the_geom,10E-10)) AS the_geom Build the polygons back up as follows SELECT a.the_geom AS the_geom, ST_pointonsurface(a.the_geom) AS point, 0 AS leftgid, 0 AS rightgid FROM (SELECT (ST_Dump(ST_polygonize(the_geom))).geom AS the_geom Then use an overlay to map the attributes back through from the left and the right. The process works, however I am getting problems with GEOS Non Noded Intersection ("GEOS union() threw an error!") crashes in some areas. These can often be fixed by rearranging the data (importing in a different order, snapping to a slightly different grid etc...). When a failure occurs I am given two linestrings and a point, however these usually bear no relationship to the lines in either the expected output, the left or the right side other than being in the same area. Unfortunately I can't provide data at the moment as any attempt to reduce the size of the dataset seems to remove (or relocate) the problem. I will try and get permission to release some data from the customer, but this will take some time. One thing to note is that the layers I am combining contain very complex and very similar linework. It would not be unexpected to get 10 sets of similar but not identical linework all running around an area. This is acceptable for the end product, but I am wondering if it is upsetting the Union somehow? If anyone has any ideas they would be most appreciated. Cheers, James Sewell Developer LISAsoft ________________________________ Ph: +61 3 8680 3250 Fax: +61 3 8680 3299 Level 9, 601 Bourke St, Melbourne Vic 3000 ________________________________ LISAsoft is part of the A2end Group of Companies http://www.ardec.com.au<http://www.ardec.com.au/> http://www.lisasoft.com<http://www.lisasoft.com/> http://www.terrapages.com<http://www.terrapages.com/> _______________________________________________ geos-devel mailing list geos-devel@lists.osgeo.org<mailto:geos-devel@lists.osgeo.org> http://lists.osgeo.org/mailman/listinfo/geos-devel No virus found in this message. Checked by AVG - www.avg.com<http://www.avg.com> Version: 10.0.1191 / Virus Database: 1435/3373 - Release Date: 01/11/11
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