Martin, <br>after you have done the buffering operation (as Moritz said), and transformed vector map (buffer_areas) in raster (<a href="http://v.to">v.to</a> rast), you can easily extract only the interested areas by using a mapalgebra operation.. for example:<br>
<br>if "agri" is the map of your agricultural areas (green map)<br>and "buff" is the map of the buffer around the vector points<br><br>you can type: <br><br>r.mapcalc "interested_areas = agri * buff"<br>
<br> all cells with a not-zero value are the interested areas..<br>(I usually prefer to use NULL rather than ZERO.. if you prefer it too, you can use r.null to transform ZERO to NULL values)<br><br>Hope this helps!<br><br>
Annalisa<br><br><br><br><div class="gmail_quote">2009/4/23 Martin Schweizer <span dir="ltr"><<a href="mailto:schweizermartin@students.unibe.ch">schweizermartin@students.unibe.ch</a>></span><br><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">
Hi Moritz<br>
<br>
Thanks for your help. The problem is, that not each pixel around a point<br>
(city) can be used as agricultural land. So I can't simply buffer the<br>
cities with a circle. To concretize what i mean, i made a picture:<br>
<a href="http://www.fotos-hochladen.net/view/landandcity1hjbk4qy3.jpg" target="_blank">http://www.fotos-hochladen.net/view/landandcity1hjbk4qy3.jpg</a> in green<br>
you see the potential agricultural land and the black point is a city....<br>
<br>
Thanks a lot<br>
<br>
Martin<br>
<br>
Moritz Lennert schrieb:<br>
<div><div></div><div class="h5">> On 22/04/09 20:39, Martin Schweizer wrote:<br>
>> Hi<br>
>><br>
>> I have a question which is a bit complex. Hope i can describe it ;-).<br>
>><br>
>> I have a point-vector layer (the citis) and a raster layer with 1 and<br>
>> ZERO cells (The potenial agricultural land). One categorie in the vector<br>
>> layer is the land (Squaremeter) that hast to be cultivated for each<br>
>> point (city). The question is now: How can I calculate and display,<br>
>> which cells of the raster map (potential agricultural land) hast to be<br>
>> cultivated? Must be some sort of buffer or neighbourhood.....?<br>
><br>
> Assuming that this agricultural land is the same in all directions of<br>
> the city, create a column which contains the radius of the circle that<br>
> encompasses the land needed (i.e. if my memories of geometry are<br>
> correct: sqrt(surface/pi) and feed the name of this column to the<br>
> bufcol= parameter of v.buffer (or feed the formula directly to the<br>
> bufcol parameter, but this only works if you use a db-backend which<br>
> has a sqrt function, i.e. PostgreSQL).<br>
><br>
> Moritz<br>
><br>
<br>
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