[QGIS-trac] Re: [Quantum GIS] #2921: Avoid intersection of new polygons.. IS BROKEN

[Quantum GIS]

#2921: Avoid intersection of new polygons.. IS BROKEN
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   Reporter:  pinux                                      |              Owner:  nobody       
       Type:  bug                                        |             Status:  new          
   Priority:  critical: causes crash or data corruption  |          Milestone:  Version 1.6.0
  Component:  Digitising                                 |            Version:  1.5.0        
   Keywords:  intersection, polygons                     |   Platform_version:               
   Platform:  Windows                                    |           Must_fix:  Yes          
Status_info:  0                                          |  
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Comment(by pinux):

 Replying to [comment:1 mhugent]:
 > I cannot entirely follow your description. Do you mean that the merge
 tool and avoid intersection tools don't work with invalid geometries? And
 after you fixed the geometry errors on the polygons, it did work?
 > If yes, that's the behaviour I would expect. Because merge and avoid
 intersection use geos and I'm pretty sure it does not do union or
 difference on invalid geometries. Maybe postgis tests the geometries first
 and tries to fix them automatically?
 My problem is not with the merge, when I was trying to merge polygons that
 I had digitized with the option "Avoid intersection of new polygons" I had
 some errors. So i have made some view to understand what was happening
 with my data.
 And I have found that the option "Avoid intersection of new polygons" is
 not working correctly:[[BR]]
 1. If I do an union in postgis I have 2 holes,[[BR]]
 2. Polygons are overlapping;[[BR]]
 3. Polygons with multiple ring, even if I don't have digitized polygons
 with multiple rings.[[BR]]
 If you load the sql that I have uploaded you will see what I'm talking
 about.[[BR]]
 The result with 12 polygons:[[BR]]
 - union with 2 holes[[BR]]
 - 9 polygons are overlapping[[BR]]
 - 2 polygon with multiple ring[[BR]]

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Ticket URL: <http://trac.osgeo.org/qgis/ticket/2921#comment:2>
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