[GRASS-user] v.generalize issue

Roger André randre at gmail.com
Tue Oct 25 17:07:55 EDT 2011

Hello GRASS Community,

I'm having a problem that I'm hoping you can help me find the source of.

I think that either A) I am trying to use the v.generalize tool incorrectly,
B) that my data has some sort of topological problem which I'm unaware of,
or C) that there is a bug in v.generalize.  The simplest way to describe
what's happening is that I am consistently unable to generalize a large
group of contiguous polygons (African states most recently) without losing a
large number of polygons from my data.  I have tried a variety of different
things, all without success, and now I'd like to ask if someone would be
willing to verify that what I'm seeing isn't a problem of my own
creation.  I've
posted my data files at
along with a before-and-after image of the specific problem I've
encountered.  I'm using GRASS v 6.4.1 which I downloaded from the main
website 2 months ago.  The commands I have used are the following:

v.in.ogr dsn=africa_clean.shp
v.clean tool=rmarea type=boundary thresh=200000000 in=africa_clean
v.generalize type=boundary method=lang threshold=.015 look_ahead=11
in=africa_clip out=africa_general

Note:  I know that I am removing small polygons with the v.clean operation.
 My concern is with the many missing contiguous polygons in the main part of
the continent.

Thanks in advance for any help you can provide,

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