Visualize the slope gradient (Hangneigung)

To outline the steepness of a slope by colorizing the map is much simpler than I thought. The GDAL utilities have it built in (http://www.gdal.org/gdaldem.html)

Therefore it is the same process as creating the hillshading. The raw data is again the SRTM data which origins from a NASA shuttle mission in 2000. You can download this data as *.hgt.zip files.

Assuming that you have all needed files in a directory, you can create the slope gradient visualization like this:


#!/bin/bash
 for FILENAME in $(find /opt/mapnik/data/shades/raw/raw -name "*.hgt.zip")
    do
        echo $FILENAME
        /opt/mapnik/data/shades/raw/srtm_generate_hdr.sh $FILENAME
        FILEBASENAME="`basename $FILENAME .hgt.zip`"
        rm $FILEBASENAME.prj
        rm $FILEBASENAME.hgt
        rm $FILEBASENAME.bil
        rm $FILEBASENAME.hdr
        gdal_translate -of GTiff -co "TILED=YES" -a_srs "+proj=latlong" $FILEBASENAME.tif ${FILEBASENAME}_adapted.tif
        rm $FILEBASENAME.tif
        gdalwarp -of GTiff -co "TILED=YES" -srcnodata 32767 -t_srs "+proj=merc +ellps=sphere +R=6378137 +a=6378137 +units=m" -rcs -order 3 -tr 30 30 -multi ${FILEBASENAME}_adapted.tif ${FILEBASENAME}_warped.tif
        rm $FILEBASENAME_adapted.tif
        gdaldem slope ${FILEBASENAME}_warped.tif ${FILEBASENAME}_slope.tif
        rm ${FILEBASENAME}_warped.tif
        gdaldem color-relief ${FILEBASENAME}_slope.tif color_slope2.txt rendered/${FILEBASENAME}_slopecolor.tif
        rm ${FILEBASENAME}_slope.tif
    done

The *_slopecolor.tif files contain the colors for the slope gradient.

Here is where I got the information from, this post explains how to set the colors: http://blog.thematicmapping.org/2012/06/creating-color-relief-and-slope-shading.html