[GRASS-user] [GRASS-dev] how to make non-merged buffers?

[Markus Metz]

On Tue, Jun 4, 2013 at 7:54 PM, Michael Barton <Michael.Barton at asu.edu> wrote:
> So this is odd.
>
> I have 166 points, with a few cases where 2 points are in the same location
> I created a set of circular buffers around the points with
>
> v.buffer -t input=neolithic_sites type=point output=sites5km distance=5000
>
> This indeed created a set of overlapping (non-merged), circular buffers.
>
> BUT, it creates 212 areas and 100 islands according to the command output and metadata report (v.report).
>
> There are only 166 attribute table entries.
>
> So what are the extra areas and the islands?

The 7.0 -t flag preserves the categories of the input features and
cleans topology. Areas in the output can have more categories, one for
each input feature in case of overlapping buffers. This also means
that in case of overlapping buffers there are more output areas than
input features, but you have clean topology and you can extract single
buffers. See the example in the 7.0 manual.

Markus M
>
> Michael
> ____________________
> C. Michael Barton
> Director, Center for Social Dynamics & Complexity
> Professor of Anthropology, School of Human Evolution & Social Change
> Arizona State University
>
> voice:  480-965-6262 (SHESC), 480-727-9746 (CSDC)
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>
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> On Jun 3, 2013, at 12:20 AM, Markus Metz <markus.metz.giswork at gmail.com> wrote:
>
>> On Mon, Jun 3, 2013 at 1:08 AM, Hamish <hamish_b at yahoo.com> wrote:
>>> Michael wrote:
>>>>> Is there a way to create buffers around features that
>>>>> overlap when the features are near to each other instead of
>>>>> merging?
>>>
>>> Markus M wrote:
>>>> In GRASS 7, with v.buffer -t
>>>
>>> for the sake of completeness, in 6.3.0 you could do this with
>>> the debug= option, but that did not continue into the replacement
>>> 6.4 module. There you'd have to run it in a loop then combine with
>>> v.patch.
>>
>> To be precise, the 6.3 debug= option as well as the v.patch solution
>> produce really overlapping areas with broken topology. The 7.0 -t flag
>> preserves the categories of the input features and cleans topology.
>> Areas in the output can have more categories, one for each input
>> feature in case of overlapping buffers. Thus you have clean topology
>> and you can extract single buffers. See the example in the 7.0 manual.
>>
>> Markus M
>