[geos-devel] RE: GEOS errors from PostGIS
Martin Davis
mtnclimb at telus.net
Fri Jan 14 01:11:45 EST 2011
In the case of lines, I think GEOS Unary Union just delegates to
union(lines, empty point). So you could try running st_union(lines,
empty point) and see if that works.
If this doesn't work, it could just be a case where the snapping
heuristic tolerances aren't being set large enough to handle the
linework. Or, it could be some other limitation...
If the problem persists, if you can send me a sample dataset (as
shapefile or WKB file) which shows the problem, I can try and see if JTS
has the same problem and if there's an obvious fix.
Martin
On 1/13/2011 9:54 PM, James.Sewell at lisasoft.com wrote:
>
> 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-bounces at lists.osgeo.org
> [mailto:geos-devel-bounces at lists.osgeo.org] *On Behalf Of *Martin Davis
> *Sent:* Friday, 14 January 2011 2:51 PM
> *To:* geos-devel at 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
> <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.Sewell at lisasoft.com
> <mailto:James.Sewell at 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.Sewell at lisasoft.com <mailto:James.Sewell at lisasoft.com>
> *Sent:* Wednesday, 12 January 2011 12:06 PM
> *To:* 'geos-devel at lists.osgeo.org <mailto:geos-devel at 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/>
>
>
>
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