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

GEOS geos-trac at osgeo.org
Fri Jun 4 16:32:53 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 mdavis):

 The result is reflecting the fact that the vertices of the two polygons
 are slightly different to each other.  In fact polygon A has a vertex
 which creates a triangle  slightly outside polygon B.  The difference is
 so small that the triangle collapses to a line.  (See attached image).

 The overlay algorithm is able to compute geometry for these situations,
 and optionally provide it (as a way of seeing where collapses have
 occurred).  As Paul said, for backwards compatibility reasons by default
 the collapses are returned in the result.

Ticket URL: <https://trac.osgeo.org/geos/ticket/1031#comment:5>
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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