[GRASS-user] large shapefile not importing properly with v.import

[Markus Metz]

On Fri, Oct 20, 2017 at 8:22 PM, Helmut Kudrnovsky <hellik at web.de> 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
> grass-user at lists.osgeo.org
> https://lists.osgeo.org/mailman/listinfo/grass-user
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.osgeo.org/pipermail/grass-user/attachments/20171020/c5990e69/attachment.html>