Provided by: gdal-bin_2.4.2+dfsg-1build2_amd64 bug

NAME

       gdaldem - Tools to analyze and visualize DEMs.

SYNOPSIS

       - To generate a shaded relief map from any GDAL-supported elevation raster :
           gdaldem hillshade input_dem output_hillshade
                       [-z ZFactor (default=1)] [-s scale* (default=1)]"
                       [-az Azimuth (default=315)] [-alt Altitude (default=45)]
                       [-alg ZevenbergenThorne] [-combined | -multidirectional]
                       [-compute_edges] [-b Band (default=1)] [-of format] [-co "NAME=VALUE"]* [-q]

       - To generate a slope map from any GDAL-supported elevation raster :
           gdaldem slope input_dem output_slope_map"
                       [-p use percent slope (default=degrees)] [-s scale* (default=1)]
                       [-alg ZevenbergenThorne]
                       [-compute_edges] [-b Band (default=1)] [-of format] [-co "NAME=VALUE"]* [-q]

       - To generate an aspect map from any GDAL-supported elevation raster
         Outputs a 32-bit float raster with pixel values from 0-360 indicating azimuth :
           gdaldem aspect input_dem output_aspect_map"
                       [-trigonometric] [-zero_for_flat]
                       [-alg ZevenbergenThorne]
                       [-compute_edges] [-b Band (default=1)] [-of format] [-co "NAME=VALUE"]* [-q]

       - To generate a color relief map from any GDAL-supported elevation raster
           gdaldem color-relief input_dem color_text_file output_color_relief_map
                       [-alpha] [-exact_color_entry | -nearest_color_entry]
                       [-b Band (default=1)] [-of format] [-co "NAME=VALUE"]* [-q]
           where color_text_file contains lines of the format "elevation_value red green blue"

       - To generate a Terrain Ruggedness Index (TRI) map from any GDAL-supported elevation raster:
           gdaldem TRI input_dem output_TRI_map
                       [-compute_edges] [-b Band (default=1)] [-of format] [-q]

       - To generate a Topographic Position Index (TPI) map from any GDAL-supported elevation raster:
           gdaldem TPI input_dem output_TPI_map
                       [-compute_edges] [-b Band (default=1)] [-of format] [-q]

       - To generate a roughness map from any GDAL-supported elevation raster:
           gdaldem roughness input_dem output_roughness_map
                       [-compute_edges] [-b Band (default=1)] [-of format] [-q]

       Notes :
         gdaldem generally assumes that x, y and z units are identical.  If x (east-west)
         and y (north-south) units are identical, but z (elevation) units are different, the
         scale (-s) option can be used to set the ratio of vertical units to horizontal.  For
         LatLong projections near the equator, where units of latitude and units of
         longitude are similar, elevation (z) units can be converted to be compatible
         by using scale=370400 (if elevation is in feet) or scale=111120 (if elevation is in
         meters).  For locations not near the equator, it would be best to reproject your
         grid using gdalwarp before using gdaldem..fi

DESCRIPTION

       This utility has 7 different modes :

       hillshade
           to generate a shaded relief map from any GDAL-supported elevation raster

       slope
           to generate a slope map from any GDAL-supported elevation raster

       aspect
           to generate an aspect map from any GDAL-supported elevation raster

       color-relief
           to generate a color relief map from any GDAL-supported elevation raster

       TRI
           to generate a map of Terrain Ruggedness Index from any GDAL-supported elevation raster

       TPI
           to generate a map of Topographic Position Index from any GDAL-supported elevation
           raster

       roughness
           to generate a map of roughness from any GDAL-supported elevation raster

       The following general options are available :

       input_dem:
           The input DEM raster to be processed

       output_xxx_map:
           The output raster produced

       -of format:
           Select the output format. Starting with GDAL 2.3, if not specified, the format is
           guessed from the extension (previously was GTiff). Use the short format name.

       -compute_edges:
           (GDAL >= 1.8.0) Do the computation at raster edges and near nodata values

       -alg ZevenbergenThorne:
           (GDAL >= 1.8.0) Use Zevenbergen & Thorne formula, instead of Horn's formula, to
           compute slope & aspect. The literature suggests Zevenbergen & Thorne to be more suited
           to smooth landscapes, whereas Horn's formula to perform better on rougher terrain.

       -b band:
           Select an input band to be processed. Bands are numbered from 1.

       -co 'NAME=VALUE':
           Passes a creation option to the output format driver. Multiple -co options may be
           listed. See format specific documentation for legal creation options for each format

       -q:
           Suppress progress monitor and other non-error output.

       For all algorithms, except color-relief, a nodata value in the target dataset will be
       emitted if at least one pixel set to the nodata value is found in the 3x3 window centered
       around each source pixel. The consequence is that there will be a 1-pixel border around
       each image set with nodata value. From GDAL 1.8.0, if -compute_edges is specified, gdaldem
       will compute values at image edges or if a nodata value is found in the 3x3 window, by
       interpolating missing values.

Modes

   hillshade
       This command outputs an 8-bit raster with a nice shaded relief effect. It’s very useful
       for visualizing the terrain. You can optionally specify the azimuth and altitude of the
       light source, a vertical exaggeration factor and a scaling factor to account for
       differences between vertical and horizontal units.

       The value 0 is used as the output nodata value.

       The following specific options are available :

       -z zFactor:
           vertical exaggeration used to pre-multiply the elevations

       -s scale:
           ratio of vertical units to horizontal. If the horizontal unit of the source DEM is
           degrees (e.g Lat/Long WGS84 projection), you can use scale=111120 if the vertical
           units are meters (or scale=370400 if they are in feet)

       -az azimuth:
           azimuth of the light, in degrees. 0 if it comes from the top of the raster, 90 from
           the east, ... The default value, 315, should rarely be changed as it is the value
           generally used to generate shaded maps.

       -alt altitude:
           altitude of the light, in degrees. 90 if the light comes from above the DEM, 0 if it
           is raking light.

       -combined:
           (starting with GDAL 1.10) combined shading, a combination of slope and oblique
           shading.

       -multidirectional:
           (starting with GDAL 2.2) multidirectional shading, a combination of hillshading
           illuminated from 225 deg, 270 deg, 315 deg, and 360 deg azimuth.

       Multidirectional hillshading applies the formula of
       http://pubs.usgs.gov/of/1992/of92-422/of92-422.pdf.

   slope
       This command will take a DEM raster and output a 32-bit float raster with slope values.
       You have the option of specifying the type of slope value you want: degrees or percent
       slope. In cases where the horizontal units differ from the vertical units, you can also
       supply a scaling factor.

       The value -9999 is used as the output nodata value.

       The following specific options are available :

       -p :
           if specified, the slope will be expressed as percent slope. Otherwise, it is expressed
           as degrees

       -s scale:
           ratio of vertical units to horizontal. If the horizontal unit of the source DEM is
           degrees (e.g Lat/Long WGS84 projection), you can use scale=111120 if the vertical
           units are meters (or scale=370400 if they are in feet)

   aspect
       This command outputs a 32-bit float raster with values between 0° and 360° representing
       the azimuth that slopes are facing. The definition of the azimuth is such that : 0° means
       that the slope is facing the North, 90° it's facing the East, 180° it's facing the South
       and 270° it's facing the West (provided that the top of your input raster is north
       oriented). The aspect value -9999 is used as the nodata value to indicate undefined aspect
       in flat areas with slope=0.

       The following specifics options are available :

       -trigonometric:
           return trigonometric angle instead of azimuth. Thus 0° means East, 90° North, 180°
           West, 270° South

       -zero_for_flat:
           return 0 for flat areas with slope=0, instead of -9999

       By using those 2 options, the aspect returned by gdaldem aspect should be identical to the
       one of GRASS r.slope.aspect. Otherwise, it's identical to the one of Matthew Perry's
       aspect.cpp utility.

   color-relief
       This command outputs a 3-band (RGB) or 4-band (RGBA) raster with values are computed from
       the elevation and a text-based color configuration file, containing the association
       between various elevation values and the corresponding wished color. By default, the
       colors between the given elevation values are blended smoothly and the result is a nice
       colorized DEM. The -exact_color_entry or -nearest_color_entry options can be used to avoid
       that linear interpolation for values that don't match an index of the color configuration
       file.

       The following specifics options are available :

       color_text_file:
           text-based color configuration file

       -alpha :
           add an alpha channel to the output raster

       -exact_color_entry :
           use strict matching when searching in the color configuration file. If none matching
           color entry is found, the '0,0,0,0' RGBA quadruplet will be used

       -nearest_color_entry :
           use the RGBA quadruplet corresponding to the closest entry in the color configuration
           file.

       The color-relief mode is the only mode that supports VRT as output format. In that case,
       it will translate the color configuration file into appropriate LUT elements. Note that
       elevations specified as percentage will be translated as absolute values, which must be
       taken into account when the statistics of the source raster differ from the one that was
       used when building the VRT.

       The text-based color configuration file generally contains 4 columns per line : the
       elevation value and the corresponding Red, Green, Blue component (between 0 and 255). The
       elevation value can be any floating point value, or the nv keyword for the nodata value..
       The elevation can also be expressed as a percentage : 0% being the minimum value found in
       the raster, 100% the maximum value.

       An extra column can be optionally added for the alpha component. If it is not specified,
       full opacity (255) is assumed.

       Various field separators are accepted : comma, tabulation, spaces, ':'.

       Common colors used by GRASS can also be specified by using their name, instead of the RGB
       triplet. The supported list is : white, black, red, green, blue, yellow, magenta, cyan,
       aqua, grey/gray, orange, brown, purple/violet and indigo.

       Since GDAL 1.8.0, GMT .cpt palette files are also supported (COLOR_MODEL = RGB only).

       Note: the syntax of the color configuration file is derived from the one supported by
       GRASS r.colors utility. ESRI HDR color table files (.clr) also match that syntax. The
       alpha component and the support of tab and comma as separators are GDAL specific
       extensions.

       For example :

       3500   white
       2500   235:220:175
       50%   190 185 135
       700    240 250 150
       0      50  180  50
       nv     0   0   0   0

   TRI
       This command outputs a single-band raster with values computed from the elevation. TRI
       stands for Terrain Ruggedness Index, which is defined as the mean difference between a
       central pixel and its surrounding cells (see Wilson et al 2007, Marine Geodesy 30:3-35).

       The value -9999 is used as the output nodata value.

       There are no specific options.

   TPI
       This command outputs a single-band raster with values computed from the elevation. TPI
       stands for Topographic Position Index, which is defined as the difference between a
       central pixel and the mean of its surrounding cells (see Wilson et al 2007, Marine Geodesy
       30:3-35).

       The value -9999 is used as the output nodata value.

       There are no specific options.

   roughness
       This command outputs a single-band raster with values computed from the elevation.
       Roughness is the largest inter-cell difference of a central pixel and its surrounding
       cell, as defined in Wilson et al (2007, Marine Geodesy 30:3-35).

       The value -9999 is used as the output nodata value.

       There are no specific options.

C API

       Starting with GDAL 2.1, this utility is also callable from C with GDALDEMProcessing().

AUTHORS

       Matthew Perry perrygeo@gmail.com, Even Rouault even.rouault@mines-paris.org, Howard Butler
       hobu.inc@gmail.com, Chris Yesson chris.yesson@ioz.ac.uk

       Derived from code by Michael Shapiro, Olga Waupotitsch, Marjorie Larson, Jim Westervelt :
       U.S. Army CERL, 1993. GRASS 4.1 Reference Manual. U.S. Army Corps of Engineers,
       Construction Engineering Research Laboratories, Champaign, Illinois, 1-425.

See also

       Documentation of related GRASS utilities :

       http://grass.osgeo.org/grass64/manuals/html64_user/r.slope.aspect.html

       http://grass.osgeo.org/grass64/manuals/html64_user/r.shaded.relief.html

       http://grass.osgeo.org/grass64/manuals/html64_user/r.colors.html