Importing polygons

Susan Huse sue at
Tue Aug 3 20:17:34 EDT 1993

> From grass-lists-owner at Tue Aug  3 15:08:01 1993
> Date: Tue, 3 Aug 93 16:50:49 CDT
> From: mg at (Mark S. Gregory)
> Sender: grass-lists-owner at
> Reply-To: grassu-list at
> To: grassu-list at
> Subject: Importing polygons
> Content-Length: 807
> I have received some data in which all of the areas are defined as polygons.
> Even those areas which have common edges with other areas are contained as
> complete polygons.
> I can import the polygons into GRASS without any trouble.  I would, however,
> like to convert the polygons to 'area edges' or segments in the manner that
> GRASS stores areas.  Manually 'breaking the lines' in v.digit, then 'snapping'
> the nodes, and removing the multiple lines (the common borders) is a tedious,
> imprecise and often very complicated operation.  Am I missing something in
> GRASS that would make this easier?
> Any thoughts on the subject would be greatly appreciated.
> Mark Gregory                    mg at
> Oklahoma State University       (405)744-6417
> Stillwater, OK 74078            (405)744-5269  fax

	v.spag -i threshold=0
take care of this???   In theory it would create nodes at each of
the overlapping polygon intersections, and then cut out the duplicate
area edges.  I have had good luck in general with v.spag -i, however, 
I generally have to do a little cleaning to correct for "almost"
identical lines etc.  Give it a shot (on a copy of course) and 
good luck.

Sue Huse
UC Berkeley.

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