Importing polygons

[Susan Huse]

> From grass-lists-owner at max.cecer.army.mil Tue Aug  3 15:08:01 1993
> Date: Tue, 3 Aug 93 16:50:49 CDT
> From: mg at adasn4.agr.okstate.edu (Mark S. Gregory)
> Sender: grass-lists-owner at max.cecer.army.mil
> Reply-To: grassu-list at max.cecer.army.mil
> To: grassu-list at max.cecer.army.mil
> 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 adasn4.agr.okstate.edu
> Oklahoma State University       (405)744-6417
> Stillwater, OK 74078            (405)744-5269  fax
> 


Would 
	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
REGIS
UC Berkeley.