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NAME
r.shaded.relief - Creates shaded relief map from an elevation map (DEM).
KEYWORDS
raster, elevation
SYNOPSIS
r.shaded.relief
r.shaded.relief help
r.shaded.relief map=string [shadedmap=string] [altitude=float] [azimuth=float] [zmult=float] [scale=float] [units=string] [--overwrite] [--verbose] [--quiet]
Flags:
- --overwrite
- Allow output files to overwrite existing files
- --verbose
- Verbose module output
- --quiet
- Quiet module output
Parameters:
- map=string
- Input elevation map
- shadedmap=string
- Output shaded relief map name
- altitude=float
- Altitude of the sun in degrees above the horizon
- Options: 0-90
- Default: 30
- azimuth=float
- Azimuth of the sun in degrees to the east of north
- Options: 0-360
- Default: 270
- zmult=float
- Factor for exaggerating relief
- Default: 1
- scale=float
- Scale factor for converting horizontal units to elevation units
- Default: 1
- units=string
- Set scaling factor (applies to lat./long. locations only, none: scale=1)
- Options: none,meters,feet
- Default: none
DESCRIPTION
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:
-
r.shaded.relief
The program then prompts the user to enter values for:
- 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 the special case when a latitude-longitude projection is used with an
elevation map measured in meters (e.g., SRTM, ETOPO2 etc.) or feet, the
units can be set to automatically set the horizontal scale to the the number of
meters (scale=111120) or feet (scale=370400) 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 units parameter overrides the scale parameter.
- 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)
Specifically, r.shaded.relief executes a
r.mapcalc
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".
r.shaded.relief then runs r.colors
to assign 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.
FILES
This program is simply a shell script. Users are encouraged to make their
own shell scripts using similar techniques.
See $GISBASE/scripts/r.shaded.relief.
SEE ALSO
"r.mapcalc: An Algebra for GIS and Image Processing", by Michael Shapiro
and Jim Westervelt, U.S. Army Construction Engineering Research Laboratory
(March/1991) (available from the GRASS web site).
d.his,
g.region,
r.blend,
r.colors,
r.mapcalc,
r.resamp.interp
AUTHOR
Jim Westervelt, U.S. Army Construction Engineering
Research Laboratory
Last changed: $Date: 2009-05-04 00:57:21 -0700 (Mon, 04 May 2009) $
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