[GRASS-user] conditional buffering with DEM

[Moritz Lennert]

On 23/04/15 16:44, Ahmet Temiz wrote:
> thank you Nikos
>
> I meant that  creating buffers from a line, which also querying DEM values.
>
> DEM is in subquery position of buffer map

You cannot do that directly, AFAIK, but using r.mapcalc you can combine 
the two variables. Different paths are possible. Here's one (supposing a 
buffer of 500m):

- Create a raster map with distance to the line using r.grow.distance
- Use r.mapcalc in order to check for both distance and DEM value, e.g.

NewMap = if(DEM > 100 && DEM < 200 && distance < 500, 1, null())

This will give you a map with non-null (value 1) in those pixels that 
are within the buffer distance and that correspond to the DEM-related 
condition.

Is this what you are looking for ?

Another path would be combining r.buffer output with the DEM in r.mapcalc.

Moritz


>
> regards
>
> On Thu, Apr 23, 2015 at 1:28 PM, Nikos Alexandris
> <nik at nikosalexandris.net <mailto:nik at nikosalexandris.net>> wrote:
>
>     * Ahmet Temiz <ahmettemiz88 at gmail.com
>     <mailto:ahmettemiz88 at gmail.com>> [2015-04-23 12:16:49 +0300]:
>
>     > hello,
>     >
>     > Which function can we use to generate  a map that has conditional buffering
>     > according to DEM from a line ?
>
>     Hello Ahmet,
>
>     I don't understand the "from a line" part of your question. Yet, I guess
>     you mean to keep a specific range of DEM values.
>
>     You can directly use r.mapcalc for such tasks.
>
>     1) Remember to set the extent and the resolution of the active
>     computational region, it'll be also the one of the new map produced by
>     r.mapcalc
>
>     2) r.mapcalc 'NewMap = if( DEM > 100 && DEM < 200, DEM, null())'
>
>     This example will write only DEM values between '100 < DEM < 200' in the
>     "NewMap" and will set to NULL all other pixels that don't satisfy the
>     above expression.  For more, please look at r.mapcalc's manual.
>
>     Of course, all this is valid and achievable via the GUI.
>
>     Regards, Nikos
>
>
>
>
> --
> Ahmet Temiz
> Jeoloji Müh.
> Afet ve Acil Durum Yönetimi Başkanlığı
> Bilgi İşlem  Dairesi Başkanlığı-CBS Grubu
>
>
> ________________________
>
> Ahmet Temiz
> Geological Eng.
> Information Systems - GIS Group
> Disaster and Emergency Management
> of Presidency
>
>
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