Take the 2-minute tour ×
Geographic Information Systems Stack Exchange is a question and answer site for cartographers, geographers and GIS professionals. It's 100% free, no registration required.

I have a SRTM DEM and I want to create a shaded relief from it. I created the shaded relief in GRASS and the result is very nice, but a little rough becouse the area is near flat and the DEM is 90m in resolution.

What I want is to make the DEM smoother in order to generate a smooth shaded relief. Is there an algorithm or interpolation method to do that?

Here is the shaded relief to get an idea, I want to flatten these small bumps:

enter image description here

share|improve this question

3 Answers 3

up vote 23 down vote accepted

How about John Stevenson's r.denoise, from the GRASS AddOns wiki:

r.denoise denoises (smooths/despeckles) topographic data, particular DEMs derived from radar data (including SRTM), using Xianfang Sun's denoising algorithm. It is designed to preserve sharp edges and to denoise with minimal changes to the original data.


I read further from this website (that I also give credit for the above animation) that a more generic method would be to use an Esri ASCII Grid file. The location of mdenoise (downloaded from Sun's website) needs to be in your PATH variable (e.g., Windows users: drop MDenoise.exe in the bin folder with your OSGeo4w or FWTools install). Then, for example, you can use the following shell command to process the ASCII grid file:

# gdal_translate -of AAIGrid my_dem.tif my_dem.asc      # convert to .asc
mdenoise -i my_dem.asc -n 5 -t 0.99 -o my_dem_DN.asc    # denoise
# gdal_translate -of GTiff my_dem_DN.asc my_dem_DN.tif  # convert back to .tif
share|improve this answer
Any python / gdal portage ? –  Hugolpz May 6 at 12:47
You can always run any command from Python. –  Mike T May 7 at 5:53

In ArcMap I like to use the Spatial Analyst>focal statistics tool to smooth out lidar prior to making contours...this might also help in your hillshading case. It's a similar function to the above post I believe.

share|improve this answer
oops, just read the GRASS part...well I'm sure there is a similar operation... –  aug_aug Jul 29 '11 at 21:49

You could run a simple filter on the DEM - say, a 5x5 moving window average filter.

share|improve this answer

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.