Re: [GRASS-user] GRASS64 - r.mapcalc - replacement of specifics value by a mean of nearest neigbour
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 ___ grass-user mailing list grass-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-user
Re: [GRASS-user] GRASS64 - r.mapcalc - replacement of specifics value by a mean of nearest neigbour
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 ___ grass-user mailing list grass-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-user
Re: [GRASS-user] GRASS64 - r.mapcalc - replacement of specifics value by a mean of nearest neigbour
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 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 ___ grass-user mailing list grass-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-user ___ grass-user mailing list grass-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-user
[GRASS-user] GRASS64 - r.mapcalc - replacement of specifics value by a mean of nearest neigbour
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 ___ grass-user mailing list grass-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-user
