I'm trying to make a decent-looking shaded-relief map of a particular area in 50K-scale-or-larger using open-source tools. The best (and free) option I have for DEM data for that area right now is the global 90m resolution SRTM3 data.

So far I have tried using GDAL tools (gdalbuildvrt,gdalwarp,gdal_translate,gdaldem) and GRASS tools (r.resamp.rst,r.shaded.relief) to produce the shaded-relief. But the output always retained these characteristics:

  • Image is too pixelated at 50K-scale-or-larger. I've tried re-sampling them to 30m and even 5m using RST/bilinear/cubic methods, but the images are somehow still pixelated
  • The landform is not clear or too generalized. I have to increase the z-factor up-to 4.0 to obtain better landform. I don't know if this is normal..

I've read most of the work done by Tom Patterson in http://www.reliefshading.com and http://www.shadedrelief.com, and I'm trying to emulate his work - but I realized that most of the pointers he gave revolved around small-scale maps, and the use of propriety softwares to get the job done (I can only afford to use open-source stuff for now). So I'm at a lost right now.. Perhaps the enhancement for the SRTM3 DEM can be done in GIMP somehow?

So my ultimate question: is it possible to make use of SRTM3 data to make a decent 50K-scale-or-larger shaded-relief maps? If I can, how should I go about processing it?

Appreciate any leads on this matter, thanks!

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    The SRTM 90 m. data is probably too coarse for a good looking elevation map at the scale you want. You might try to increase the resolution of the SRTM data with r.resamp.rst. Set the ewres and nsres to something like 10 meters. The result might "look nice" but I'm not sure how true to the actual terrain it will be. Additionally there;s the ASTER DEM data with global coverage at 30 m. resolution. Maybe that will work better. – Micha Nov 15 '12 at 6:47
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    See here for an example of shaded ASTER DEM: gis.cri.fmach.it/aster-gdem-quality – markusN Nov 15 '12 at 7:13
  • Thanks @markusN for the link! Those GRASS notes at the end should be useful! – user8723 Nov 15 '12 at 7:33

We had good results with this approach:

  1. Convert original raster DEM (90 meters) to points
  2. Interpolate points to a new raster (finer resolution e.g. 10 meters)
  3. Create hillshade from new raster (step 2).

It was a few years ago - so I can not remember the parameters exactly. But I guess we used a spline interpolation. Spline produced very soft surfaces. Spline well closed holes in the original raster DEM.

  • I'm having trouble figuring out how to do Step 1 in your suggested approach.. Step 2 and 3 won't be a problem, I guess.. – user8723 Nov 16 '12 at 2:00
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    I did the analysis with ArcGIS. I do not know grass. But I assume that grass can do a raster do vector (point) conversion. Perhaps with the r.to.vect command? – Jens Nov 16 '12 at 8:53
  • Oh yeah.. r.to.vect should do it, silly me.. Thanks again @Jens – user8723 Nov 16 '12 at 11:05

Although Patterson's method is described with Photoshop, Gimp works too. From a thumbnail overview of the Resolution Bumping Shaded Relief I wrote a few years ago:

Load the relief image in GIMP (created from gdaldem after using @Jens dem>points>dem method):

  • duplicate layer
  • upper layer == the detail layer, leave alone, set Mode to Overlay
  • bottom == the shape layer,\ apply Gaussian blur with setting 20
  • save a copy (relief_blurred.tif)

Re-assign projection (using a small gdal python script, a copy here):

gdalcopyproj shaded_relief.tif relief_blurred.tif

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