[QGIS-trac] [Quantum GIS] #1865: ftools "Union" gives wrong results with non overlapping polygons

[Quantum GIS]

#1865: ftools "Union" gives wrong results with non overlapping polygons
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   Reporter:  lutra                                           |              Owner:  cfarmer      
       Type:  bug                                             |             Status:  new          
   Priority:  critical: causes crash or data corruption       |          Milestone:  Version 1.2.0
  Component:  Python plugins and bindings                     |            Version:  HEAD         
   Keywords:  geoprocessing, overlay, union, non-overlapping  |   Platform_version:               
   Platform:  All                                             |           Must_fix:  No           
Status_info:  0                                               |  
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 I'm not sure to classify this as "critical" but as the resulting attribute
 tables are wrong seems to me "data corruption". If I'm wrong please change
 the priority of the ticket.

 I noticed that applying the ftools "Union" tool to non overlapping
 polygons (if the polygons do overlap then results are ok) returns *always*
 a wrong attribute table.

 The "old" geoprocessing tool plugin gives better results, as it does GRASS
 v.overlay.or

 I was playing around with different polygon layers with different table of
 attributes (that for the "Union" operation does not make a lot of
 difference), so I also noticed that in the same case (non overlapping
 polygons) when the two attribute tables have different column names but
 same types then both the "old" geoprocessing tool plugin and GRASS
 v.overlay.or do an error.

 I compared with the results given by the Union tool of Arcgis 9.x and
 gvSIG and in this case the results are ok with both software, so if ftools
 is going to be fixed then would be better to avoid the error made by the
 other two qgis solutions.

 See attached files.

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Ticket URL: <https://trac.osgeo.org/qgis/ticket/1865>
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