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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 entered 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 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.

       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.resamp.interp

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: 2018-10-26 15:33:19 +0200 (Fri, 26 Oct 2018) $

SOURCE CODE

       Available at: r.relief source code (history)

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       © 2003-2019 GRASS Development Team, GRASS GIS 7.6.1 Reference Manual