a problem with r.poly?

[A.B. South]

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I wonder if anyone can help. I've been trying to use r.poly to 
create vector format areas from simple raster polygons (3-10 vertices).
In some, but not all, cases the outline of the polygon is created 
but with an additional line going from one of the vertices down to 
the base of the region. Is this a problem anyone else has 
encountered? Is there a way of getting around it?

The polygons were originally created from a series of coordinates 
in a text file using r.in.poly. Decreasing the resolution at which 
this is carried out cures the problem in some cases but not others.

Alternatively can anyone suggest another way of converting a series 
of coordinates of vertices into raster and vector polygons?

Thanks in advance.

Andy South
University of Newcastle-upon-Tyne
A.B.South at ncl.ac.uk