On Fri, Oct 20, 2017 at 8:22 PM, Helmut Kudrnovsky <[email protected]> wrote: > > >I have what I think is a large shapefile. It is 122 MB (30 MB dbf file and > 90 MB shp file). > > not that large; a few weeks ago I've imported a ~1 GB shapefile; it took > some time to import because of topological building, but it worked. > > >WARNING: Number of incorrect boundaries: 1586 > >WARNING: Number of centroids outside area: 186 > >WARNING: Number of duplicate centroids: 631 > > it seems there may be some issues e.g. overlapping polygons, > self-intersections of boundaries, very small areas etc. > > try to use v.in.ogr instead in a location with the original projection and > then reproject it. > > sometimes I get data sets with such warnings; first I open such data in > QGIS; in master aka QGIS 3, there is a nice new topology checker to inspect > about topological errors. after some cleaning in QGIS, I try to import the > data by v.in.ogr without cleaning and afterwards clean the vector data by > v.clean e.g. remove small areas, etc
The cleaning part of v.in.ogr should be renamed to "converting non-topological polygons to topological areas areas". The real cleaning happens only if the snap option is set to > 0. v.in.ogr should provide a topologically correct vector map. Overlapping areas are ok if the input polygons are really supposed to overlap. Can you provide examples where v.in.ogr with cleaning/polygon conversion did not work, but v.in.ogr -c + v.clean produced better results? This would help to improve v.in.ogr, which should be able to produce a reasonable output, maybe with some parameter tuning. I noticed that v.in.ogr complains about overlapping areas, which were input polygons that should not overlap, but snapping did not help there, instead I needed to remove small areas afterwards with v.clean. Should the current min_area option of v.in.ogr also be used to remove small areas in the output? Markus M > > HTH > > > > > > > ----- > best regards > Helmut > -- > Sent from: http://osgeo-org.1560.x6.nabble.com/Grass-Users-f3884509.html > _______________________________________________ > grass-user mailing list > [email protected] > https://lists.osgeo.org/mailman/listinfo/grass-user
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