gdaldem(1)

1gdaldem(1)                  General Commands Manual                 gdaldem(1)
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NAME

6       gdaldem - .TH "gdaldem" 1 "Fri Apr 22 2011" "GDAL"
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NAME

9       gdaldem - Tools to analyze and visualize DEMs. (since GDAL 1.7.0)
10

SYNOPSIS

12       - To generate a shaded relief map from any GDAL-supported elevation raster :
13           gdaldem hillshade input_dem output_hillshade
14                       [-z ZFactor (default=1)] [-s scale* (default=1)]"
15                       [-az Azimuth (default=315)] [-alt Altitude (default=45)]
16                       [-b Band (default=1)] [-of format] [-co "NAME=VALUE"]* [-q]
17
18       - To generate a slope map from any GDAL-supported elevation raster :
19           gdaldem slope input_dem output_slope_map"
20                       [-p use percent slope (default=degrees)] [-s scale* (default=1)]
21                       [-b Band (default=1)] [-of format] [-co "NAME=VALUE"]* [-q]
22
23       - To generate an aspect map from any GDAL-supported elevation raster
24         Outputs a 32-bit float raster with pixel values from 0-360 indicating azimuth :
25           gdaldem aspect input_dem output_aspect_map"
26                       [-trigonometric] [-zero_for_flat]
27                       [-b Band (default=1)] [-of format] [-co "NAME=VALUE"]* [-q]
28
29       - To generate a color relief map from any GDAL-supported elevation raster
30           gdaldem color-relief input_dem color_text_file output_color_relief_map
31                       [-alpha] [-exact_color_entry | -nearest_color_entry]
32                       [-b Band (default=1)] [-of format] [-co "NAME=VALUE"]* [-q]
33           where color_text_file contains lines of the format "elevation_value red green blue"
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35       - To generate a Terrain Ruggedness Index (TRI) map from any GDAL-supported elevation raster:
36           gdaldem TRI input_dem output_TRI_map
37                       [-b Band (default=1)] [-of format] [-q]
38
39       - To generate a Topographic Position Index (TPI) map from any GDAL-supported elevation raster:
40           gdaldem TPI input_dem output_TPI_map
41                       [-b Band (default=1)] [-of format] [-q]
42
43       - To generate a roughness map from any GDAL-supported elevation raster:
44           gdaldem roughness input_dem output_roughness_map
45                       [-b Band (default=1)] [-of format] [-q]
46
47       Notes :
48         Scale is the ratio of vertical units to horizontal
49          for Feet:Latlong use scale=370400, for Meters:LatLong use scale=111120)
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51

DESCRIPTION

53       This utility has 7 different modes :
54
55       hillshade
56           to generate a shaded relief map from any GDAL-supported elevation
57           raster
58
59       slope
60           to generate a slope map from any GDAL-supported elevation raster
61
62       aspect
63           to generate an aspect map from any GDAL-supported elevation raster
64
65       color-relief
66           to generate a color relief map from any GDAL-supported elevation
67           raster
68
69       TRI
70           to generate a map of Terrain Ruggedness Index from any GDAL-
71           supported elevation raster
72
73       TPI
74           to generate a map of Topographic Position Index from any GDAL-
75           supported elevation raster
76
77       roughness
78           to generate a map of roughness from any GDAL-supported elevation
79           raster
80
81       The following general options are available :
82
83       input_dem:
84           The input DEM raster to be processed
85
86       output_xxx_map:
87           The output raster produced
88
89       -of format:
90           Select the output format. The default is GeoTIFF (GTiff). Use the
91           short format name.
92
93       -b band:
94           Select an input band to be processed. Bands are numbered from 1.
95
96       -co 'NAME=VALUE':
97           Passes a creation option to the output format driver. Multiple -co
98           options may be listed. See format specific documentation for legal
99           creation options for each format.
100
101       -q:
102           Suppress progress monitor and other non-error output.
103

Modes

105   hillshade
106       This command outputs an 8-bit raster with a nice shaded relief effect.
107       It’s very useful for visualizing the terrain. You can optionally
108       specify the azimuth and altitude of the light source, a vertical
109       exaggeration factor and a scaling factor to account for differences
110       between vertical and horizontal units.
111
112       The following specific options are available :
113
114       -z zFactor:
115           vertical exaggeration used to pre-multiply the elevations
116
117       -s scale:
118           ratio of vertical units to horizontal. If the horizontal unit of
119           the source DEM is degrees (e.g Lat/Long WGS84 projection), you can
120           use scale=111120 if the vertical units are meters (or scale=370400
121           if they are in feet)
122
123       -az azimuth:
124           azimuth of the light, in degrees. 0 if it comes from the top of the
125           raster, 90 from the east, ... The default value, 315, should rarely
126           be changed as it is the value generally used to generate shaded
127           maps.
128
129       -alt altitude:
130           altitude of the light, in degrees. 90 if the light comes from above
131           the DEM, 0 if it is raking light.
132
133   slope
134       This command will take a DEM raster and output a 32-bit float raster
135       with slope values. You have the option of specifying the type of slope
136       value you want: degrees or percent slope. In cases where the horizontal
137       units differ from the vertical units, you can also supply a scaling
138       factor.
139
140       The following specific options are available :
141
142       -p :
143           if specified, the slope will be expressed as percent slope.
144           Otherwise, it is expressed as degrees
145
146       -s scale:
147           ratio of vertical units to horizontal. If the horizontal unit of
148           the source DEM is degrees (e.g Lat/Long WGS84 projection), you can
149           use scale=111120 if the vertical units are meters (or scale=370400
150           if they are in feet)
151
152   aspect
153       This command outputs a 32-bit float raster with values between 0° and
154       360° representing the azimuth that slopes are facing. The definition of
155       the azimuth is such that : 0° means that the slope is facing the North,
156       90° it's facing the East, 180° it's facing the South and 270° it's
157       facing the West (provided that the top of your input raster is north
158       oriented). The aspect value -9999 is used as the nodata value to
159       indicate undefined aspect in flat areas with slope=0.
160
161       The following specifics options are available :
162
163       -trigonometric:
164           return trigonometric angle instead of azimuth. Thus 0° means East,
165           90° North, 180° West, 270° South
166
167       -zero_for_flat:
168           return 0 for flat areas with slope=0, instead of -9999
169
170       By using those 2 options, the aspect returned by gdaldem aspect should
171       be identical to the one of GRASS r.slope.aspect. Otherwise, it's
172       identical to the one of Matthew Perry's aspect.cpp utility.
173
174   color-relief
175       This command outputs a 3-band (RGB) or 4-band (RGBA) raster with values
176       are computed from the elevation and a text-based color configuration
177       file, containing the association between various elevation values and
178       the corresponding wished color. By default, the colors between the
179       given elevation values are blended smoothly and the result is a nice
180       colorized DEM. The -exact_color_entry or -nearest_color_entry options
181       can be used to avoid that linear interpolation for values that don't
182       match an index of the color configuration file.
183
184       The following specifics options are available :
185
186       color_text_file:
187           text-based color configuration file
188
189       -alpha :
190           add an alpha channel to the output raster
191
192       -exact_color_entry :
193           use strict matching when searching in the color configuration file.
194           If none matching color entry is found, the '0,0,0,0' RGBA
195           quadruplet will be used
196
197       -nearest_color_entry :
198           use the RGBA quadruplet corresponding to the closest entry in the
199           color configuration file.
200
201       The color-relief mode is the only mode that supports VRT as output
202       format. In that case, it will translate the color configuration file
203       into appropriate <LUT> elements. Note that elevations specified as
204       percentage will be translated as absolute values, which must be taken
205       into account when the statistics of the source raster differ from the
206       one that was used when building the VRT.
207
208       The text-based color configuration file generally contains 4 columns
209       per line : the elevation value and the corresponding Red, Green, Blue
210       component (between 0 and 255). The elevation value can be any floating
211       point value, or the nv keyword for the nodata value.. The elevation can
212       also be expressed as a percentage : 0% being the minimum value found in
213       the raster, 100% the maximum value.
214
215       An extra column can be optionnaly added for the alpha component. If it
216       is not specified, full opacity (255) is assumed.
217
218       Various field separators are accepted : comma, tabulation, spaces, ':'.
219
220       Common colors used by GRASS can also be specified by using their name,
221       instead of the RGB triplet. The supported list is : white, black, red,
222       green, blue, yellow, magenta, cyan, aqua, grey/gray, orange, brown,
223       purple/violet and indigo.
224
225       Note: the syntax of the color configuration file is derived from the
226       one supported by GRASS r.colors utility. ESRI HDR color table files
227       (.clr) also match that syntax. The alpha component and the support of
228       tablulations and commma as separators are GDAL specific extensions.
229
230       For example :
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232       3500   white
233       2500   235:220:175
234       50%   190 185 135
235       700    240 250 150
236       0      50  180  50
237       nv     0   0   0   0
238
239
240   TRI
241       This command outputs a single-band raster with values computed from the
242       elevation. TRI stands for Terrain Ruggedness Index, which is defined as
243       the mean difference between a central pixel and its surrounding cells
244       (see Wilson et al 2007, Marine Geodesy 30:3-35).
245
246       There are no specific options.
247
248   TPI
249       This command outputs a single-band raster with values computed from the
250       elevation. TPI stands for Topographic Position Index, which is defined
251       as the difference between a central pixel and the mean of its
252       surrounding cells (see Wilson et al 2007, Marine Geodesy 30:3-35).
253
254       There are no specific options.
255
256   roughness
257       This command outputs a single-band raster with values computed from the
258       elevation. Roughness is the the largest inter-cell difference of a
259       central pixel and its surrounding cell, as defined in Wilson et al
260       (2007, Marine Geodesy 30:3-35).
261
262       There are no specific options.
263

AUTHORS

265       Matthew Perry <perrygeo@gmail.com>, Even Rouault <even.rouault@mines-
266       paris.org>, Howard Butler <hobu.inc@gmail.com>, Chris Yesson
267       <chris.yesson@ioz.ac.uk>
268
269       Derived from code by Michael Shapiro, Olga Waupotitsch, Marjorie
270       Larson, Jim Westervelt : U.S. Army CERL, 1993. GRASS 4.1 Reference
271       Manual. U.S. Army Corps of Engineers, Construction Engineering Research
272       Laboratories, Champaign, Illinois, 1-425.
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NAME

NAME

SYNOPSIS

DESCRIPTION

Modes

AUTHORS

See also