On Thu Jun 26 15:31 , Moritz Lennert
On 26/06/08 08:49, Richard Chirgwin wrote:
Moritz Lennert wrote:
On 25/06/08 02:46, Richard Chirgwin wrote:
Hi all,
- v.overlay question
I have three maps: two area vectors (A and B), and a v.overlay result
(C). Is there a simple way to assign the percentage of areas in (A)
covered by the overlay (C)?
Vector solution:
http://lists.osgeo.org/pipermail/grass-user/2008-June/045290.html
Moritz
Moritz,
This led me straight into an oddity. One of my vectors is created by
buffering around points.
The source map was a set of 800 points. V.buffer runs successfully, and
when it ends, the new areas display without problem. However, when I run
v.db.addtable, there are only 18 categories - any ideas?
As GRASS is topologically clean, areas cannot overlap. v.buffer,
therefore, fusions those buffers that do. So if your 800 points are
close enough to each other to make the buffers overlap, they might
result in only 18 distinct polygons. This should be visible when you
display them.
Moritz
Moritz,
Alas, no. These are small polygons - there is one area where overlap exists, but there are still hundreds of distinct polygons. This is busting my brain…
Richard
On 26/06/08 10:01, rchirgwin@ozemail.com.au wrote:
On Thu Jun 26 15:31 , Moritz Lennert sent:
On 26/06/08 08:49, Richard Chirgwin wrote:
> Moritz Lennert wrote:
>> On 25/06/08 02:46, Richard Chirgwin wrote:
>>> Hi all,
>>>
>>> 1) v.overlay question
>>>
>>> I have three maps: two area vectors (A and B), and a v.overlay
result
>>> (C). Is there a simple way to assign the percentage of areas in
(A)
>>> covered by the overlay (C)?
>>
>> Vector solution:
>>
http://lists.osgeo.org/pipermail/grass-user/2008-June/045290.html
<parse.pl?redirect=http%3A%2F%2Flists.osgeo.org%2Fpipermail%2Fgrass-user%2F2008-June%2F045290.html>
>>
>> Moritz
>>
> Moritz,
>
> This led me straight into an oddity. One of my vectors is created by
> buffering around points.
>
> The source map was a set of 800 points. V.buffer runs
successfully, and
> when it ends, the new areas display without problem. However,
when I run
> v.db.addtable, there are only 18 categories - any ideas?
As GRASS is topologically clean, areas cannot overlap. v.buffer,
therefore, fusions those buffers that do. So if your 800 points are
close enough to each other to make the buffers overlap, they might
result in only 18 distinct polygons. This should be visible when you
display them.
Moritz
Moritz,
Alas, no. These are small polygons - there is one area where overlap
exists, but there are still hundreds of distinct polygons. This is
busting my brain...
Sorry, didn't watch out: actually v.buffer gives each buffer the same category, so it's funny that you see 18 categories...
If you want to transfer the categories of the points to the buffers, see the example "Non-overlapping circles around input points with attribute transfer" in the man page.
Moritz