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

[Markus Metz]

On Wed, Apr 20, 2011 at 2:21 PM, Hanlie Pretorius
<hanlie.pretorius at gmail.com> wrote:
> 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 bug concerning the southwest corner is already fixed in 6.5,
awaiting ok for backport to 6.4.2.

The 3 other corners are also incorrect, I guess they should be
rounded. At least they are with other areas of similar shape.

Markus M


> 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
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