[geos-devel] [GEOS] #1031: Union of two Polygons results in GeometryCollection

GEOS geos-trac at osgeo.org
Fri Jun 4 16:17:45 PDT 2021

#1031: Union of two Polygons results in GeometryCollection
 Reporter:  brownjt     |       Owner:  geos-devel@…
     Type:  defect      |      Status:  closed
 Priority:  minor       |   Milestone:  3.10.0
Component:  Default     |     Version:  3.8.0
 Severity:  Unassigned  |  Resolution:  invalid
 Keywords:              |

Comment (by brownjt):

 Replying to [comment:2 pramsey]:
 > Have a look at OverlayNG.setStrictMode(). If you turn on strict mode,
 the results of overlays will only include components of a single
 dimensionality. Unfortunately (?) the results of the standard methods on
 Geometry have to match up to the old behaviour for legacy reasons, so
 strict mode is turned off by default.

 I don't understand how this is invalid. The issue is not with the
 dimensionality of the result. There should be only one resulting geometry
 from the union not two. It has been some time since I looked at this but I
 believe the extra line string actually has duplicate points that are
 already present on the resulting polygon. Why is it generating these extra

Ticket URL: <https://trac.osgeo.org/geos/ticket/1031#comment:4>
GEOS <http://trac.osgeo.org/geos>
GEOS (Geometry Engine - Open Source) is a C++ port of the Java Topology Suite (JTS).

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