Hi, Thank you all for your feedback!
@Nyall - the GEOS/JTS capabilities for cleaning and validating geometries look definitely interesting. Something for an upcoming QGIS-CH grant perhaps ... @Bernhard - I also had a look at and tested the "Eliminate selected polygons" algorithm - but it doesn't have a way to specify attribute handling nor grouping - and it is also strange that I have to select the polygons first and cannot run the algorithm on the whole data set as is About SAGA: I couldn't get the SAGA stuff to work anymore About GRASS: it could be an option, but a native solution in QGIS would be preferred So in summary: there are several options around for cleaning overlaps - but it isn't as straight-forward and user friendly yet as it could/should be. I haven't looked at the gaps yet ... Thank you all and greetings, Andreas On Tue, 25 Jul 2023 at 13:13, Bernhard Ströbl via QGIS-User < qgis-user@lists.osgeo.org> wrote: > Hi Andreas, > > the Algorithm "Eliminate selected polygons" was originally created to > address these questions. I usually imported the data into GRASS ran a clean > there and reexported the results into a non topolgical dataset. Thus > overlapping areas and gaps (only if closed) are identified and can be > eliminated using the algorithm named above (selecting only a certain > area-circumference relation) by merging it with the adjacent polygon with > the smallest/largest area or the longest common boundary. > For your case you could have used this algorithm after the union to > identify overlaps. > As for an algorithm that does all this in one go: You would need something > that detects holes between polygons without the help of a toplogical data > format. > > regards > Bernhard > > > Andreas Neumann via QGIS-User <qgis-user@lists.osgeo.org> hat am > 25.07.2023 12:01 CEST geschrieben: > > > > > > Hi, > > > > A friend of mine has a dirty input data set with lots of overlapping > > geometries (within the same layer) and asked me if there is a tool > > within QGIS to automatically remove the overlaps and assign the > > overlapping area to the neighbor polygon with the largest area. > > > > The solution was surprisingly hard to find, although I am pretty sure > > there are multiple combinations of algorithms that would solve the > > problem. Here is the solution I came up with: > > https://github.com/qgis-ch/overlap_removal/tree/main [1]- perhaps you > > have better ideas - more elegant solutions? > > > > Wouldn't it be great if QGIS had a processing tool to solve this overlap > > cleaning within the same layer "out of the box" without having to use a > > graphical model or a more or less complicated sequence of algorithms in > > the processing toolbox? Apparently, ArcGIS has such a tool ... > > > > Saga and GRASS also might have such tools - but I couldn't get the SAGA > > based QGIS plugin "Dissect and dissolve overlaps" > > (https://plugins.qgis.org/plugins/dissect_dissolve_overlaps). > > > > The same problem exists for automatically filling small gaps in the > > polygon data set ... > > > > Andreas > > > > > > > > Links: > > ------ > > [1] > https://github.com/qgis-ch/overlap_removal/tree/main_______________________________________________ > > QGIS-User mailing list > > QGIS-User@lists.osgeo.org > > List info: https://lists.osgeo.org/mailman/listinfo/qgis-user > > Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-user > _______________________________________________ > QGIS-User mailing list > QGIS-User@lists.osgeo.org > List info: https://lists.osgeo.org/mailman/listinfo/qgis-user > Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-user > -- -- Andreas Neumann QGIS.ORG board member (treasurer)
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