r.shaded.relief - Creates shaded relief map from an elevation map (DEM).
r.shaded.relief map=string [shadedmap=string] [altitude=integer] [azimuth=integer] [zmult=float] [scale=float] [units=string] [--overwrite]
- Force overwrite of output files
- Input elevation map
- Output shaded relief map name
- Altitude of the sun in degrees above the horizon
- Options: 0-90
- Default: 30
- Azimuth of the sun in degrees to the east of north
- Options: 0-360
- Default: 270
- Factor for exaggerating relief
- Default: 1
- Scale factor for converting horizontal units to elevation units
- Default: 1
- Set scaling factor (applies to lat./long. locations only)
- Options: meters,feet
r.shaded.relief is a Bourne shell script that
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.
If no parameters are provided on startup, this program is interactive;
thus if the user enters the command:
The program then prompts the user to enter values for:
Specifically, r.shaded.relief executes a
statement. Refer to the manual entry for
r.mapcalc for an explanation
of the filtering syntax shown in the above expression.
See, for example, the section on "The Neighborhood Modifier".
- The altitude of the sun in degrees above the horizon
(a value between 0 and 90 degrees), and
- The azimuth of the sun in degrees to the east of north
(a value between 0 and 360 degrees).
- The name of 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.
- 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.)
For ETOPO2 data a scale factor of 10000 generates an acceptable
- For the special case when a latitude-longitude projection is used
with an elevation map measured in meters or feet, the units can
be set to automatically set the horizontal scale to the the number of
meters or feet in a degree of latitude. The script scales latitude and
longitude equally, so it's only approximately right, but for shading
it's close enough. It makes the difference between a usable and unusable shade.
- 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)
r.shaded.relief then runs r.colors
to assign a grey-scale color table to the new shaded relief map.
This program is simply a shell script. Users are encouraged to make their
own shell scripts using similar techniques.
An Algebra for GIS and Image Processing, by Michael Shapiro and Jim
Westervelt, U.S. Army Construction Engineering Research Laboratory
(March/1991) (get from GRASS web site).
Jim Westervelt, U.S. Army Construction Engineering
Last changed: $Date: 2006/04/20 02:43:23 $
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