[GRASS-user] Two questions - vector data and Mac install

[Moritz Lennert]

On 26/06/08 10:01, rchirgwin at 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