Ciao Vero, shapefile is not a good choice in this case for exporting such geometry because is not apt to store topological information. You may want to export your dataset in a different format, e.g. geopackage.
Hope this helps, On Tue, May 14, 2019 at 11:47 PM Veronica Andreo <veroand...@gmail.com> wrote: > Hi all, > > I was working today with a very simple vector map which corresponds to > clusters (circular polygons) that overlap and it is just fine that they > overlap. So, i received a shapefile with 3 of these clusters. Two of them > overlaped. When I import them into GRASS with v.import I get an extra > centroid and area where 2 of the polygons overlap. > > Problem arises when I want to query a raster map with those polygons since > originally the attribute table contained only 3 polygons (which is just > fine). However, v.what.rast will only upload values for 2 of those three > polygons because it finds 2 centroids with the same category, AFAIU. > > I tried with > > v.clean input=clusters output=clusters_clean1 tool=break,rmdupl,rmsa,rmdac > > and > > v.clean input=clusters type=centroid output=clusters_clean2 tool=rmdupl > > but nothing seemed to do the kind of cleaning I wanted. I ended up using > brute force and removing the extra centroid manually in the GUI. That > helped with v.what.rast (all cats in the attr table were updated) but part > of the original and correct geometry was clearly gone. I am sure that's not > the right combination nor the right way either. > > In the wiki [0], I only found this piece of text: "If the *input polygons > have logical errors*.... You can investigate overlapping areas in the > imported vector with 'd.vect > <https://grass.osgeo.org/grass76/manuals/d.vect.html> yourmap type=area > layer=2' (only overlapping areas have a category in layer 2 after import). > Additionally you may show the centroids of layer=2 to easier find tiny > overlapping areas with 'd.vect > <https://grass.osgeo.org/grass76/manuals/d.vect.html> yourmap > type=centroid layer=2'" > > However, it says nothing about how to proceed further as to keep correctly > overlapping polygons, each with its own centroid and remove the duplicated > ones that are generated when importing. > > Can someone please share the set of steps that should be followed in these > cases? Maybe it's a silly question, but I'm more a raster person so I am > very easily lost with vector issues. > > Thanks much in advance! > Vero > > [0] https://grasswiki.osgeo.org/wiki/Vector_topology_cleaning > _______________________________________________ > grass-user mailing list > grass-user@lists.osgeo.org > https://lists.osgeo.org/mailman/listinfo/grass-user -- Margherita Di Leo
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