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 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
.shade. The map is assigned a grey-scale color
table.
The module then prompts the user to enter values for:
- 1
- The altitude of the sun in degrees above the horizon
(a value between 0 and 90 degrees), and
- 2
- The azimuth of the sun in degrees to the east of
north (a value between 0 and 360 degrees).
- 3
- 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.
- 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
- 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.
- 6
- 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.
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 map=elevation shadedmap=elevation.shaded
In Latitude-Longitude locations (or other non-metric locations), the
scale factor has to be used:
# Latitude-Longitude example
r.shaded.relief map=srtm shadedmap=srtm.shaded scale=111120
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: 2011-11-08 12:29:50 +0100 (Tue, 08 Nov 2011) $
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© 2003-2011 GRASS Development Team