Geoprocessing - Desktop GIS: Mapping the Planet with Open Source Tools - page 149

GRASS 6.2.2 (albers_c6):~ > r.shaded.relief help

Description:
Creates shaded relief map from an elevation map (DEM).

Keywords:
raster, elevation

Usage:
r.shaded.relief map=string [shadedmap=string] [altitude=value]
[azimuth=value] [zmult=value] [scale=value] [units=string]
[--overwrite]

Flags:
--o Force overwrite of output files

Parameters:
map Input elevation map

shadedmap Output shaded relief map name

altitude Altitude of the sun in degrees above the horizon

options: 0-90
default: 30

azimuth Azimuth of the sun in degrees to the east of north

options: 0-360
default: 270

zmult Factor for exaggerating relief

default: 1

scale Scale factor for converting horizontal units to elevation units

default: 1

units Set scaling factor (applies to lat./long. locations only)

options: meters,feet

The command is pretty straightforward and has several options for cre-
ating the shaded relief map from the DEM, including sun angle and
altitude. We can also exaggerate the relief to get a more dramatic effect.
We'll start simple and create a standard shaded relief map:

GRASS 6.2.2 (albers_c6):~ > r.shaded.relief map=ancc6_dem \
shadedmap=ancc6_shade1
Calculating shading, please stand by.
100%
Color table for [ancc6_shade1] set to grey

Shaded relief map created and named [ancc6_shade1].

This map is all default settings. Generally, the default light settings
(altitude and azimuth) produce good results, unless you have particular
needs. Notice that when we created the hillshade, it set the color to
gray. This is because r.shaded.relief is actually a shell script that runs
both r.mapcalc and r.colors to create the hillshade. Let's try one with