[GRASS-user] One chamfered corner with v.buffer on an extents rectangle

[Hanlie Pretorius]

Hi,

I'm working in GRASS 6.4.0 and using v.buffer applied to an extents
rectangle. For some reason v.buffer is producing one chamfered corner
in the buffered vector.

The command I used was:
v.buffer -s -c --overwrite input=c83a_extents at PERMANENT
output=c83a_extents_5km_buffer at 20m_DEM distance=5000.
Buffering lines...
Buffering areas...
Building topology for vector map <c83a_extents_5km_buffer>...
Registering primitives...
1 primitives registered
12 vertices registered
Number of nodes: 1
Number of primitives: 1
Number of points: 0
Number of lines: 0
Number of boundaries: 1
Number of centroids: 0
Number of areas: -
Number of isles: -
Snapping boundaries...
Breaking boundaries...
Removing duplicates...
Attaching islands...
Building topology for vector map <c83a_extents_5km_buffer>...
Building areas...
1 areas built
1 isles built
Attaching islands...
Number of nodes: 1
Number of primitives: 1
Number of points: 0
Number of lines: 0
Number of boundaries: 1
Number of centroids: 0
Number of areas: 1
Number of isles: 1
Number of areas without centroid: 1
Attaching centroids...
Building topology for vector map <c83a_extents_5km_buffer>...
Attaching centroids...
Number of nodes: 2
Number of primitives: 2
Number of points: 0
Number of lines: 0
Number of boundaries: 1
Number of centroids: 1
Number of areas: 1
Number of isles: 1
Building topology for vector map <c83a_extents_5km_buffer>...
Registering primitives...
2 primitives registered
13 vertices registered
Building areas...
1 areas built
1 isles built
Attaching islands...
Attaching centroids...
Number of nodes: 2
Number of primitives: 2
Number of points: 0
Number of lines: 0
Number of boundaries: 1
Number of centroids: 1
Number of areas: 1
Number of isles: 1
(Wed Apr 20 14:08:46 2011) Command finished (1 sec)

I have placed a screenshot of the outcome on the web
<http://www.nedbib.za.net/v.buffer.png>. The region was set to the DEM
raster in the background. The black triangle is the extents and the
red one the buffered polygon.

Does someone know why v.buffer would create such a chamfered corner.
I've played around with selecting different feature types and adding a
minor distance value, but I always get the same result.

Thanks
Hanlie