Ubuntu Manpage: r.relief - Creates shaded relief map from an elevation map (DEM).

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Provided by: grass-doc_7.0.3-1build1_all

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 map

       output=name [required]
           Name for output shaded relief map
           Name for output raster 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 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;
clockwise from north).

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 zscale 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.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.relief is then run on the
       resampled DEM.

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:
       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 "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

AUTHORS

       Jim Westervelt, U.S. Army Construction Engineering Research Laboratory
       Markus Metz: Enhanced fast C version of r.relief for GRASS GIS 7

       Last changed: $Date: 2015-07-11 16:04:13 +0200 (Sat, 11 Jul 2015) $

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