[geos-devel] [GEOS] #620: Incorrect intersection between geometries

GEOS geos-trac at osgeo.org
Wed Feb 6 03:34:02 PST 2013

#620: Incorrect intersection between geometries
 Reporter:  rhf         |       Owner:  geos-devel@…              
     Type:  defect      |      Status:  new                       
 Priority:  major       |   Milestone:  3.3.x                     
Component:  Default     |     Version:  3.3.7                     
 Severity:  Unassigned  |    Keywords:                            
 I have two polylines A, B which partly overlap.

 When computing the intersection C = intersection(A, B), geos reports the
 correct result, which is a simple linestring with two points.
 One of them is a noded intersection. The other one is not.

 Hereafter I compute D = intersection(B, C). Of course D should equal C.
 Instead I will only get a single point: the noded intersection.

 This seems strange to me: either I would expect C also to be incorrect or
 both queries to give the same result.
 The same issue occurs when I try to compute B - C.

 With similar cases involving a noded and none-noded intersection, I get
 the correct results in all cases. For example when trying to reproduce the
 issue with simple horizontal lines.

 I have attached to small files in WKB format: A.txt, B.txt to be used as
 input to reproduce the issue.
 Actually the original polygons used as input where much larger, but I was
 able to reduce their sizes such that they only have a few points. Also I
 am working with geos via Spatialite, but I do not think this is relevant
 for this issue.

Ticket URL: <http://trac.osgeo.org/geos/ticket/620>
GEOS <http://geos.refractions.net/>
GEOS (Geometry Engine - Open Source) is a C++ port of the Java Topology Suite (JTS).

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