[GRASS-user] buffer vector within a given area

[Martin Schweizer]

Hi Moritz

Thanks for your help. The problem is, that not each pixel around a point
(city) can be used as agricultural land. So I can't simply buffer the
cities with a circle. To concretize what i mean, i made a picture:
http://www.fotos-hochladen.net/view/landandcity1hjbk4qy3.jpg in green
you see the potential agricultural land and the black point is a city....

Thanks a lot

Martin

Moritz Lennert schrieb:
> On 22/04/09 20:39, Martin Schweizer wrote:
>> Hi
>>
>> I have a question which is a bit complex. Hope i can describe it ;-).
>>
>> I have a point-vector layer (the citis) and a raster layer with 1 and
>> ZERO cells (The potenial agricultural land). One categorie in the vector
>> layer is the land (Squaremeter) that hast to be cultivated for each
>> point (city). The question is now: How can I calculate and display,
>> which cells of the raster map (potential agricultural land) hast to be
>> cultivated? Must be some sort of buffer or neighbourhood.....?
>
> Assuming that this agricultural land is the same in all directions of
> the city, create a column which contains the radius of the circle that
> encompasses the land needed (i.e. if my memories of geometry are
> correct: sqrt(surface/pi) and feed the name of this column to the
> bufcol= parameter of v.buffer (or feed the formula directly to the
> bufcol parameter, but this only works if you use a db-backend which
> has a sqrt function, i.e. PostgreSQL).
>
> Moritz
>