Bug report #390

GEOS: TopologyException occuring with identify tool

Added by neteler-itc-it - over 16 years ago. Updated over 13 years ago.

Assignee:Gary Sherman
Affected QGIS version: Regression?:No
Operating System:All Easy fix?:No
Pull Request or Patch supplied: Resolution:fixed
Crashes QGIS or corrupts data: Copied to github as #:10449



via IRC I reported this problem and "wonder" fixed something already:

I have now recompiled QGIS and latest 2.x GEOS. The identification now seems to work,
but still these warnings appear:

Warning: GEOS: [[TopologyException]]: side location conflict (4.33168e+06,2.52514e+06)
Warning: GEOS: [[TopologyException]]: side location conflict (4.34597e+06,2.51173e+06)
Warning: GEOS: [[TopologyException]]: side location conflict (4.39699e+06,2.59723e+06)

The sample SHAPE file is here: http://mpa.itc.it/markus/tmp/qgis/
It comes with some huge multipolygons.

I also contacted strk who told me (pasted with permission):

strk*refractions.net wrote on 11.11.2006 11:32:
> The topology exceptions are not considered real bug, but rather
> a limit of the algorithms. New algorithms in GEOS-3.0.0 
> use some heuristics on exception and try to reapply the operation
> on a sligtly modified input to reduce likelyness of robustness issues.
> I think qgis should be using the C-API, where all of this comes for
> free (and GEOS-2.2.x should have the C-API already, so qgis will be
> binary compatible back to that version of geos). Alternatively you
> can probably still using the C++ api and make it compatible with both
> 2.2.x and 3.0.0 geos by adding some 'using namespace' directives IFF
> major_version > 2.
> --strk;

Best regards,


#1 Updated by Marco Hugentobler over 15 years ago

  • Resolution set to fixed
  • Status changed from Open to Closed

I'm closing this ticket as it is possible to compile and link qgis against geos 3 (with -DPEDANTIC=off)

#2 Updated by Anonymous over 13 years ago

Milestone Version 0.9 deleted

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