[GRASS-user] ... getting rid of duplicate polygons ...

[Uwe Fischer]

Hello list,

 

I have a question about dealing with duplicate polygons (dp) coming into
GRASS from a polygon shapefile. The polygons are not overlapping or having
gaps, but there are a number of real duplicate ones (polygons show parcels
with owners, and if one parcel has two or more owners, e. g. wife and
husband, this situation in the shapefile is represented by two identical
polys with two database rows that only differ in the owners name).

 

My goal is to get rid of duplicates, having a result with only one
polygon/centroid at a given location with only one owner name. The name does
not matter, it can be chosen arbitrary by the system. This works fine when
using ESRI "clean"-command. The structure of the database table is
maintained while one (or many) of the dp is/are lost, leaving only one valid
polygon.

 

Now, I found an older thread called "unable to get rid of duplicate
polygons". Obviously, the problem/question is the same but I could not find
a solution for GRASS there. So I tried:

 

v.clean -c input=input at mapset output=output_clean tool=snap,rmdac,bpol
threshold=0.01,0,0

 

and

 

v.clean -c input=input at mapset output=output_clean
tool=break,snap,rmdupl,rmdac,bpol

 

Nothing did work. I get a map with tree layers, one showing the islands only
(layer 0), one showing the complete polygon set with duplicates (1), and one
showing only the duplicates (2). I also tried to delete layer 2, assuming
that this might remove the dp, but it only messed up the dataset.

 

What am I doing wrong?

 

Regards, Uwe

 

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