[QGIS-trac] Re: [Quantum GIS] #3126: Sliver holes remain after dissolve

[Quantum GIS]

#3126: Sliver holes remain after dissolve
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        Reporter:  gislab                            |         Owner:  jef          
            Type:  bug                               |        Status:  closed       
        Priority:  major: does not work as expected  |     Milestone:  Version 1.6.0
       Component:  Vectors                           |       Version:  Trunk        
      Resolution:  invalid                           |      Keywords:               
Platform_version:                                    |      Platform:  All          
        Must_fix:  No                                |   Status_info:  0            
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Changes (by lutra):

 * cc: cfarmer (added)
  * platform:  Windows => All
  * status:  reopened => closed
  * resolution:  => invalid
  * version:  => Trunk


Comment:

 Hi gislab,
 here the following.
 [[BR]]


 The vector "1.zip" is topologically unclean, no way you can change/correct
 this in QGIS right now. It would be nice to have a tool for it, this is
 because I'll add to this ticket Carson, and eventually (if you agree) we
 can change the summary and the description to something such "add a tool
 to correct topology". I would suggest to open a new ticket, '''but if you
 feel I'm wrong just reopen this one'''.

 The situation is the following:

 AFAIK dissolve is made by GEOS and at least by default it '''does
 nothing''' (while dissolving) to correct problems like slivers/overlapping
 areas. So in any case is NOT a QGIS problem.

 You say that the same operation under Arc* gives you a clean vector, so it
 would be very interesting if you can attach the vector obtained trough the
 dissolve with arc* to give it a look.

 One more time: you vector is unclean and nor GEOS nor QGIS can do a lot
 for this (QGIS for sure, GEOS probably not). Actually this is the typical
 case we use to show how to clean vectors by using GRASS.
 [[BR]]

 Import the vector in GRASS, take the "1_polygon" layer (the one with the
 correct polygons) and then apply the '''v.clean''' module with the
 "'''rmarea'''" option. This way it will eliminate all the slivers.

 And actually this will work just fine with the vectors you posted, without
 having to leave QGIS, just use the GRASS plugin.

-- 
Ticket URL: <https://trac.osgeo.org/qgis/ticket/3126#comment:10>
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