r.relief(1grass) GRASS GIS User's Manual r.relief(1grass)
NAME
r.relief - Creates shaded relief map from an elevation map (DEM).
KEYWORDS
raster, elevation, relief, terrain, hillshade
SYNOPSIS
r.relief
r.relief --help
r.relief input=name output=name [altitude=float] [azimuth=float]
[zscale=float] [scale=float] [units=string] [--overwrite]
[--help] [--verbose] [--quiet] [--ui]
Flags:
--overwrite
Allow output files to overwrite existing files
--help
Print usage summary
--verbose
Verbose module output
--quiet
Quiet module output
--ui
Force launching GUI dialog
Parameters:
input=name [required]
Name of input raster (typically elevation) map
output=name [required]
Name for output shaded relief map
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
zscale=float
Factor for exaggerating relief
Default: 1
scale=float
Scale factor for converting meters to elevation units
Default: 1
units=string
Elevation units (overrides scale factor)
Options: intl, survey
intl: international feet
survey: survey feet
DESCRIPTION
r.relief creates a raster shaded relief map based on current resolution
settings and on sun altitude, azimuth, and z-exaggeration values en-
tered by the user.
The parameters controlling the shading are:
1 An input raster map 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; clockwise from north)
4 The scaling parameter, which compensates for a different hori-
zontal 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 zscale exaggeration factor that changes the apparent relief
for the shaded relief map. This can be any positive (or nega-
tive) 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 automati-
cally 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.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 eleva-
tion models, use r.resamp.interp with bilinear or bicubic method to re-
sample the DEM at higher resolution. r.relief is then run on the resam-
pled DEM.
The current mask is ignored.
EXAMPLES
Shaded relief map
In this example, the aspect map in the North Carolina sample dataset
location is used to hillshade the elevation map:
g.region raster=elevation -p
r.relief input=elevation output=elevation_shade
r.relief: shaded elevation map (subset)
Colorizing a shaded relief map
Color can be added later using r.shade or d.shade:
r.shade shade=elevation_shade color=elevation output=elevation_shaded
Using the scale factor in Latitude-Longitude
In Latitude-Longitude locations (or other non-metric locations), the
scale factor has to be used:
# Latitude-Longitude example
g.region raster=srtm -p
r.relief input=srtm output=srtm_shaded scale=111120
Exporting shaded relief maps to GeoTIFF
The data range of shaded relief maps usually does not permit exporting
the map to GeoTIFF format along with its associated color table due to
limitations in the GeoTIFF format.
The most simple way to export it while even reducing the file size is
to export as palette byte map. This requires a conversion done in
r.mapcalc, using the # operator to convert map category values to their
grey scale equivalents:
# using the map created above
# create new map from map category values
r.mapcalc expression="elevation_shade_byte = #elevation_shade"
# verify data range
r.info elevation_shade_byte
# assign grey color table
r.colors elevation_shade_byte color=grey
# export (optionally: createopt="COMPRESS=DEFLATE,BIGTIFF=YES")
r.out.gdal input=elevation_shade_byte createopt="COMPRESS=DEFLATE" \
output=elevation_shade.tif
# add overview images in GeoTIFF file for faster zooming
gdaladdo --config GDAL_CACHEMAX 2000 elevation_shade.tif 2 4 8 16
SEE ALSO
d.shade, d.his, g.region, r.shade, r.blend, r.colors, r.mapcalc, r.re-
samp.interp
AUTHORS
Jim Westervelt, U.S. Army Construction Engineering Research Laboratory
Markus Metz: Enhanced fast C version of r.relief for GRASS GIS 7
SOURCE CODE
Available at: r.relief source code (history)
Accessed: unknown
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GRASS 7.8.7 r.relief(1grass)
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