I'm trying to create a hillshade surface from SRTM files downloaded form Earth Explorer, but the appearance is not the expected.


It has a grainy surface that I would like eliminate to have a smoothest surface. I'm running GRASS 6.4.3. to create this.

It happen mostly in coastal areas. I've tried to use r.denoise but the result is neither the expected, maybe isn't noise the cause of this.

Any idea?

If you need more info just ask.

3 Answers 3


I suppose that it is the result of r.shaded.relief.

Have you set the correct resolution of your region of work (resolution of the SRTM layer, Res: 59.74514451 here) ?

Resolution of the SRTM layer:

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Resolution of the region:

enter image description here


enter image description here

r.shaded.relief without grainy surface with the correct resolution

enter image description here


I realised you asked about with GRASS, but you can also do this with gdaldem.

You can see the process I use for using gdaldem tools with SRTM data.


In case you are in a Latitude-Longitude location, the scale factor has to be used:

  # Latitude-Longitude example
  r.shaded.relief map=srtm shadedmap=srtm.shaded scale=111120
  • almost half year later, your comment has been very useful. :D Thanks
    – Luismi
    Commented Mar 5, 2014 at 13:14

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