## DESCRIPTION

r.shaded.relief creates a raster shaded relief map based on current resolution settings and on sun altitude, azimuth, and z-exaggeration values entered by the user. If no output shademap name is given, the new shaded relief map is named <input_map >.shade. The map is assigned a grey-scale color table.

The parameters controlling the shading are:

1. A raster map layer to provide elevation values for the shaded relief map. Typically, this would be a map layer of elevation; however, any raster map layer can be named.
2. The altitude of the sun in degrees above the horizon (a value between 0 and 90 degrees).
3. The azimuth of the sun in degrees to the east of north (a value between 0 and 360 degrees).
4. The scaling parameter, which compensates for a different horizontal scale than vertical scale. If scale is a number, then the ewres and nsres are multiplied by that scale to calculate the shading. (Default=1.0 for equivalent horizontal and vertical scales.)
5. The zmult exaggeration factor that changes the apparent relief for the shaded relief map. This can be any positive (or negative) floating point value. (Default=1.0)
6. Horizontal distances are calculated in meters, using geodesic distances for a latitude-longitude projection. With an elevation map measured in feet, the units option can be set to automatically convert meters to international feet (0.3048 meters = 1 foot) or survey feet (1200 / 3937 meters = 1 foot). The units parameter overrides the scale parameter.

r.shaded.relief assigns a grey-scale color table to the new shaded relief map.

## NOTES

To visually improve the result of shade maps from low resolution elevation models, use r.resamp.interp with bilinear or bicubic method to resample the DEM at higher resolution. r.shaded.relief is then run on the resampled DEM.

## EXAMPLES

In this example, the aspect map in the North Carolina sample dataset location is used to hillshade the elevation map:

    g.region rast=elevation -p
    r.shaded.relief input=elevation output=elevation.shaded

In Latitude-Longitude locations (or other non-metric locations), the scale factor has to be used:

    # Latitude-Longitude example
    r.shaded.relief input=srtm output=srtm.shaded scale=111120

## SEE ALSO

d.his, g.region, r.blend, r.colors, r.mapcalc, r.resamp.interp

## AUTHOR

Jim Westervelt, U.S. Army Construction Engineering Research Laboratory

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