Dear Grass users,
I'm working with rasters maps of large area and I want to calculate surface related to specific colours. Before this, I have to replace the surfaces of the rivers by the surrounding value (or the mean of the surrounding value).
I looked at the manual of r.mapcalc but I didn't found how to do this...
For instance, I want to replace all value between 4 and 7 by the mean of the value of the 4 nearest pixels.
Is there any way of doing this?
Which command shall I use then for calculating the surface for each color? r.stats? or is there a command that directly computes the surface?
Best regards
Lucien
One way to do this would be to replace all values between 4 and 7 by NULL (e.g., r.null map=yourRaster setnull=4-7). Then use r.neighbors to calculate the mean of the nearest neighbors (e.g., r.neighbors input=yourRaster output=intermediateResult size=3. Have a look at the help file of r.neighbors and the part about the size of the neighborhood and option to use a circular neighborhood). Last step, patch the two layers together (e.g, r.patch input=yourRaster,intermediateResult output=yourOutput).
As for your second question, r.stats is indeed what you are looking for I think, it calculates the surface for each categories of the input raster layer.
Rgds
Paulo
ยทยทยท
On 05/04/2013 08:17 PM, BLANDENIER Lucien wrote:
Dear Grass users,
I'm working with rasters maps of large area and I want to calculate surface related to specific colours. Before this, I have to replace the surfaces of the rivers by the surrounding value (or the mean of the surrounding value).
I looked at the manual of r.mapcalc but I didn't found how to do this...
For instance, I want to replace all value between 4 and 7 by the mean of the value of the 4 nearest pixels.
Is there any way of doing this?
Which command shall I use then for calculating the surface for each color? r.stats? or is there a command that directly computes the surface?
Best regards
Lucien
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On 04/05/13 20:17, BLANDENIER Lucien wrote:
Dear Grass users,
I'm working with rasters maps of large area and I want to calculate surface related to specific colours. Before this, I have to replace the surfaces of the rivers by the surrounding value (or the mean of the surrounding value).
I looked at the manual of r.mapcalc but I didn't found how to do this...
For instance, I want to replace all value between 4 and 7 by the mean of the value of the 4 nearest pixels.
Is there any way of doing this?
Something like this:
newMap =if(oldMap >= 4 && oldMap <=7, (oldMap[-1,0]+oldMap[0,-1]+oldMap[0,1]+oldMap[1,0])/4, oldMap)
Which command shall I use then for calculating the surface for each color?
When you say color, I suppose you mean cell values.
r.stats? or is there a command that directly computes the surface?
r.stats -a _does_ directly compute the surface.
Moritz
BLANDENIER Lucien wrote:
Dear Grass users,
I'm working with rasters maps of large area and I want to calculate surface
related to specific colours. Before this, I have to replace the surfaces of
the rivers by the surrounding value (or the mean of the surrounding value).
I looked at the manual of r.mapcalc but I didn't found how to do this...
For instance, I want to replace all value between 4 and 7 by the mean of the
value of the 4 nearest pixels.
Is there any way of doing this?
Which command shall I use then for calculating the surface for each color?
r.stats? or is there a command that directly computes the surface?
Dear Lucien,
did you get past this problem?
I think a combination of r.neighbours (to get the average values from
surrounding cells) and r.recode (for re-categorising values in your input
raster maps so as to get the desired output) + r.stats could do it.
Didn't try anything, of course -- not time.
Thanks, Nikos