[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:  mhugent               
            Type:  bug                               |        Status:  reopened              
        Priority:  major: does not work as expected  |     Milestone:  Version 1.7.0         
       Component:  Digitising                        |       Version:  Trunk                 
      Resolution:                                    |      Keywords:  intersection, polygons
Platform_version:                                    |      Platform:  All                   
        Must_fix:  Yes                               |   Status_info:  0                     
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Comment(by mhugent):

 The removePolygonIntersction method from QGIS just calls difference()
 method from geos repeatedly.

 Taking the attached shape and removing the last polygon, it seems to me
 that the polygons in that dataset are not really adjacent to each other
 (there are small legs between). You could test that with the union
 function in QGIS directly.

 Is it possible those 'legs' have been introduced by adding polygons with
 the 'topological editing' mode in QGIS? That's where r15087 enhanced the
 precision. Now I don't manage to introduce legs like that anymore. If you
 do, please send me a shapefile, a screenshot how to add the new polygon
 and the settings you used for it (e.g. snapping tolerance) used.

-- 
Ticket URL: <http://trac.osgeo.org/qgis/ticket/2921#comment:12>
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