Is it possible to produce a decent looking shaded-relief map at 50K-scale-or-larger using SRTM3 DEM?

Question

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!

Answer 1

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.

Answer 2

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