Mapping Hacks

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Chapter 6, Mapping on Your Desktop

#72 Add Relief to Your Topographic Maps

HACK

out=${dem%.dem}

gdal_translate $dem $out.tiff

r.in.gdal -o in=$out.tiff out=${out}_dem

rm $out.tiff

done

This makes importing the DEMs a piece of cake:

GRASS:~/shade > chmod +x import_dem.sh

GRASS:~/shade > ./import_dem.sh *.dem

The script will take a few moments to run, and then we will have a whole

new set of raster layers in our GRASS mapset:

GRASS:~/shade > g.list type=rast

----------------------------------------------

raster files available in mapset sderle:

hunters_pt_dem pt_bonita_dem sf_south_dem sf_topo

oakland_west_dem sf_north_dem sf_south_oe_dem

----------------------------------------------

Next, we need to stitch these DEM layers together into a single unified layer,

so that we can do shading with it. The r.patch tool does this job admirably.

Note that GRASS only does raster processing within the current region, so

the resulting layer, which we’ll call

sf_elevation, will be clipped to the box

we drew around San Francisco earlier. Make sure you list all the DEM files

on a single line, with no spaces between the commas; GRASS commands are

sensitive to whitespace. Finally, use r.colors to colorize the elevation file and

then display it on the monitor using d.rast:

GRASS:~/shade > r.patch in=pt_bonita_dem,sf_north_dem,sf_south_dem,sf_south_

oe_dem,hunters_pt_dem,oakland_west_dem out=sf_elevation

r.patch: percent ...