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


       raster, elevation


       r.shaded.relief help
       r.shaded.relief   map=string    [shadedmap=string]     [altitude=float]    [azimuth=float]
       [zmult=float]   [scale=float]   [units=string]   [--overwrite]  [--verbose]  [--quiet]

           Allow output files to overwrite existing files

           Verbose module output

           Quiet module output

           Input elevation map

           Output shaded relief map name

           Altitude of the sun in degrees above the horizon
           Options: 0-90
           Default: 30

           Azimuth of the sun in degrees to the east of north
           Options: 0-360
           Default: 270

           Factor for exaggerating relief
           Default: 1

           Scale factor for converting horizontal units to elevation units
           Default: 1

           Set scaling factor (applies to lat./long. locations only, none: scale=1)
           Options: none,meters,feet
           Default: none


       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

       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.

       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.


       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.


       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


       "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


       Jim Westervelt, U.S. Army Construction Engineering Research Laboratory

       Last changed: $Date: 2011-11-08 03:29:50 -0800 (Tue, 08 Nov 2011) $

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