[GRASS-user] How to detect/remove overlapping polygons (imported with v.in.ogr )based on the data attributes

[Veronica Andreo]

Hello Hemant,

The discussion continued in the thread you linked (see next messages in the
thread). I used the -c flag of v.in.ogr to avoid cleaning polygons when
importing the shapefile as I needed the simple features to extract zonal
stats from raster maps afterwards. Would that be useful to you too in this
case?

Vero





El sáb, 19 feb 2022 a las 0:23, B H (<hemantbist at gmail.com>) escribió:

> I have data  in a Shapefile which has genuine  cases of overlapping
> geometries. (As documented in  v.in.ogr) the common areas appear with
> multiple categories.
> I need to find these common areas and "dedupe" them.
> Currently I  export the data out via v.out.ogr and in postgis do  select
> distinct on (st_asbinary(geometrycomlum))  from tablename  order by
> priorityattribute
>
> Is there some way to either dedupe it in grass Gis itself, or have
> v.out.ogr output  some common attribute in the two geometries that
> represent the common area
> from two polygons.
> There is a similar question in this old thread. However I could not find
> the solution.
> https://lists.osgeo.org/pipermail/grass-user/2019-May/080293.html
>
>
>
>
> ---
> clip from v.in.ogr  man page describing how  the overlapping polygons are
> handled.
>
> Overlapping polygons
> When importing overlapping polygons, the overlapping parts will become new
> areas with multiple categories, one unique category for each original
> polygon. An original polygon will thus be converted to multiple areas with
> the same shared category. These multiple areas will therefore also link to
> the same entry in the attribute table. A single category value may thus
> refer to multiple non-overlapping areas which together represent the
> original polygon overlapping with another polygon. The original polygon can
> be recovered by using v.extract with the desired category value or where
> statement and the -d flag to dissolve common boundaries
> Thanks,
> Hemant
>
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