1gdaldem(1) General Commands Manual gdaldem(1)
2
6 gdaldemTools to analyze and visualize DEMs.
7
9 - To generate a shaded relief map from any GDAL-supported elevation raster :
10 gdaldem hillshade input_dem output_hillshade
11 [-z ZFactor (default=1)] [-s scale* (default=1)]"
12 [-az Azimuth (default=315)] [-alt Altitude (default=45)]
13 [-alg ZevenbergenThorne] [-combined | -multidirectional]
14 [-compute_edges] [-b Band (default=1)] [-of format] [-co "NAME=VALUE"]* [-q]
15 - To generate a slope map from any GDAL-supported elevation raster :
17 gdaldem slope input_dem output_slope_map"
18 [-p use percent slope (default=degrees)] [-s scale* (default=1)]
19 [-alg ZevenbergenThorne]
20 [-compute_edges] [-b Band (default=1)] [-of format] [-co "NAME=VALUE"]* [-q]
21 - To generate an aspect map from any GDAL-supported elevation raster
23 Outputs a 32-bit float raster with pixel values from 0-360 indicating azimuth :
24 gdaldem aspect input_dem output_aspect_map"
25 [-trigonometric] [-zero_for_flat]
26 [-alg ZevenbergenThorne]
27 [-compute_edges] [-b Band (default=1)] [-of format] [-co "NAME=VALUE"]* [-q]
28 - 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"
34 - To generate a Terrain Ruggedness Index (TRI) map from any GDAL-supported elevation raster:
36 gdaldem TRI input_dem output_TRI_map
37 [-compute_edges] [-b Band (default=1)] [-of format] [-q]
38 - To generate a Topographic Position Index (TPI) map from any GDAL-supported elevation raster:
40 gdaldem TPI input_dem output_TPI_map
41 [-compute_edges] [-b Band (default=1)] [-of format] [-q]
42 - To generate a roughness map from any GDAL-supported elevation raster:
44 gdaldem roughness input_dem output_roughness_map
45 [-compute_edges] [-b Band (default=1)] [-of format] [-q]
46 Notes :
48 gdaldem generally assumes that x, y and z units are identical. If x (east-west)
49 and y (north-south) units are identical, but z (elevation) units are different, the
50 scale (-s) option can be used to set the ratio of vertical units to horizontal. For
51 LatLong projections near the equator, where units of latitude and units of
52 longitude are similar, elevation (z) units can be converted to be compatible
53 by using scale=370400 (if elevation is in feet) or scale=111120 (if elevation is in
54 meters). For locations not near the equator, it would be best to reproject your
55 grid using gdalwarp before using gdaldem..fi
56
58 This utility has 7 different modes :
59 hillshade
61 to generate a shaded relief map from any GDAL-supported elevation
62 raster
63 slope
65 to generate a slope map from any GDAL-supported elevation raster
66 aspect
68 to generate an aspect map from any GDAL-supported elevation raster
69 color-relief
71 to generate a color relief map from any GDAL-supported elevation
72 raster
73 TRI
75 to generate a map of Terrain Ruggedness Index from any GDAL-
76 supported elevation raster
77 TPI
79 to generate a map of Topographic Position Index from any GDAL-
80 supported elevation raster
81 roughness
83 to generate a map of roughness from any GDAL-supported elevation
84 raster
85 The following general options are available :
87 input_dem:
89 The input DEM raster to be processed
90 output_xxx_map:
92 The output raster produced
93 -of format:
95 Select the output format. Starting with GDAL 2.3, if not specified,
96 the format is guessed from the extension (previously was GTiff).
97 Use the short format name.
98 -compute_edges:
100 (GDAL >= 1.8.0) Do the computation at raster edges and near nodata
101 values
102 -alg ZevenbergenThorne:
104 (GDAL >= 1.8.0) Use Zevenbergen & Thorne formula, instead of Horn's
105 formula, to compute slope & aspect. The literature suggests
106 Zevenbergen & Thorne to be more suited to smooth landscapes,
107 whereas Horn's formula to perform better on rougher terrain.
108 -b band:
110 Select an input band to be processed. Bands are numbered from 1.
111 -co 'NAME=VALUE':
113 Passes a creation option to the output format driver. Multiple -co
114 options may be listed. See format specific documentation for legal
115 creation options for each format
116 -q:
118 Suppress progress monitor and other non-error output.
119 For all algorithms, except color-relief, a nodata value in the target
121 dataset will be emitted if at least one pixel set to the nodata value
122 is found in the 3x3 window centered around each source pixel. The
123 consequence is that there will be a 1-pixel border around each image
124 set with nodata value. From GDAL 1.8.0, if -compute_edges is specified,
125 gdaldem will compute values at image edges or if a nodata value is
126 found in the 3x3 window, by interpolating missing values.
127
129 hillshade
130 This command outputs an 8-bit raster with a nice shaded relief effect.
131 It’s very useful for visualizing the terrain. You can optionally
132 specify the azimuth and altitude of the light source, a vertical
133 exaggeration factor and a scaling factor to account for differences
134 between vertical and horizontal units.
135 The value 0 is used as the output nodata value.
137 The following specific options are available :
139 -z zFactor:
141 vertical exaggeration used to pre-multiply the elevations
142 -s scale:
144 ratio of vertical units to horizontal. If the horizontal unit of
145 the source DEM is degrees (e.g Lat/Long WGS84 projection), you can
146 use scale=111120 if the vertical units are meters (or scale=370400
147 if they are in feet)
148 -az azimuth:
150 azimuth of the light, in degrees. 0 if it comes from the top of the
151 raster, 90 from the east, ... The default value, 315, should rarely
152 be changed as it is the value generally used to generate shaded
153 maps.
154 -alt altitude:
156 altitude of the light, in degrees. 90 if the light comes from above
157 the DEM, 0 if it is raking light.
158 -combined:
160 (starting with GDAL 1.10) combined shading, a combination of slope
161 and oblique shading.
162 -multidirectional:
164 (starting with GDAL 2.2) multidirectional shading, a combination of
165 hillshading illuminated from 225 deg, 270 deg, 315 deg, and 360 deg
166 azimuth.
167 Multidirectional hillshading applies the formula of
169 http://pubs.usgs.gov/of/1992/of92-422/of92-422.pdf.
170 slope
172 This command will take a DEM raster and output a 32-bit float raster
173 with slope values. You have the option of specifying the type of slope
174 value you want: degrees or percent slope. In cases where the horizontal
175 units differ from the vertical units, you can also supply a scaling
176 factor.
177 The value -9999 is used as the output nodata value.
179 The following specific options are available :
181 -p :
183 if specified, the slope will be expressed as percent slope.
184 Otherwise, it is expressed as degrees
185 -s scale:
187 ratio of vertical units to horizontal. If the horizontal unit of
188 the source DEM is degrees (e.g Lat/Long WGS84 projection), you can
189 use scale=111120 if the vertical units are meters (or scale=370400
190 if they are in feet)
191 aspect
193 This command outputs a 32-bit float raster with values between 0° and
194 360° representing the azimuth that slopes are facing. The definition of
195 the azimuth is such that : 0° means that the slope is facing the North,
196 90° it's facing the East, 180° it's facing the South and 270° it's
197 facing the West (provided that the top of your input raster is north
198 oriented). The aspect value -9999 is used as the nodata value to
199 indicate undefined aspect in flat areas with slope=0.
200 The following specifics options are available :
202 -trigonometric:
204 return trigonometric angle instead of azimuth. Thus 0° means East,
205 90° North, 180° West, 270° South
206 -zero_for_flat:
208 return 0 for flat areas with slope=0, instead of -9999
209 By using those 2 options, the aspect returned by gdaldem aspect should
211 be identical to the one of GRASS r.slope.aspect. Otherwise, it's
212 identical to the one of Matthew Perry's aspect.cpp utility.
213 color-relief
215 This command outputs a 3-band (RGB) or 4-band (RGBA) raster with values
216 are computed from the elevation and a text-based color configuration
217 file, containing the association between various elevation values and
218 the corresponding wished color. By default, the colors between the
219 given elevation values are blended smoothly and the result is a nice
220 colorized DEM. The -exact_color_entry or -nearest_color_entry options
221 can be used to avoid that linear interpolation for values that don't
222 match an index of the color configuration file.
223 The following specifics options are available :
225 color_text_file:
227 text-based color configuration file
228 -alpha :
230 add an alpha channel to the output raster
231 -exact_color_entry :
233 use strict matching when searching in the color configuration file.
234 If none matching color entry is found, the '0,0,0,0' RGBA
235 quadruplet will be used
236 -nearest_color_entry :
238 use the RGBA quadruplet corresponding to the closest entry in the
239 color configuration file.
240 The color-relief mode is the only mode that supports VRT as output
242 format. In that case, it will translate the color configuration file
243 into appropriate LUT elements. Note that elevations specified as
244 percentage will be translated as absolute values, which must be taken
245 into account when the statistics of the source raster differ from the
246 one that was used when building the VRT.
247 The text-based color configuration file generally contains 4 columns
249 per line : the elevation value and the corresponding Red, Green, Blue
250 component (between 0 and 255). The elevation value can be any floating
251 point value, or the nv keyword for the nodata value.. The elevation can
252 also be expressed as a percentage : 0% being the minimum value found in
253 the raster, 100% the maximum value.
254 An extra column can be optionally added for the alpha component. If it
256 is not specified, full opacity (255) is assumed.
257 Various field separators are accepted : comma, tabulation, spaces, ':'.
259 Common colors used by GRASS can also be specified by using their name,
261 instead of the RGB triplet. The supported list is : white, black, red,
262 green, blue, yellow, magenta, cyan, aqua, grey/gray, orange, brown,
263 purple/violet and indigo.
264 Since GDAL 1.8.0, GMT .cpt palette files are also supported
266 (COLOR_MODEL = RGB only).
267 Note: the syntax of the color configuration file is derived from the
269 one supported by GRASS r.colors utility. ESRI HDR color table files
270 (.clr) also match that syntax. The alpha component and the support of
271 tab and comma as separators are GDAL specific extensions.
272 For example :
274 3500 white
276 2500 235:220:175
277 50% 190 185 135
278 700 240 250 150
279 0 50 180 50
280 nv 0 0 0 0
281 TRI
284 This command outputs a single-band raster with values computed from the
285 elevation. TRI stands for Terrain Ruggedness Index, which is defined as
286 the mean difference between a central pixel and its surrounding cells
287 (see Wilson et al 2007, Marine Geodesy 30:3-35).
288 The value -9999 is used as the output nodata value.
290 There are no specific options.
292 TPI
294 This command outputs a single-band raster with values computed from the
295 elevation. TPI stands for Topographic Position Index, which is defined
296 as the difference between a central pixel and the mean of its
297 surrounding cells (see Wilson et al 2007, Marine Geodesy 30:3-35).
298 The value -9999 is used as the output nodata value.
300 There are no specific options.
302 roughness
304 This command outputs a single-band raster with values computed from the
305 elevation. Roughness is the largest inter-cell difference of a central
306 pixel and its surrounding cell, as defined in Wilson et al (2007,
307 Marine Geodesy 30:3-35).
308 The value -9999 is used as the output nodata value.
310 There are no specific options.
312
314 Starting with GDAL 2.1, this utility is also callable from C with
315 GDALDEMProcessing().
316
318 Matthew Perry perrygeo@gmail.com, Even Rouault even.rouault@mines-
319 paris.org, Howard Butler hobu.inc@gmail.com, Chris Yesson
320 chris.yesson@ioz.ac.uk
321 Derived from code by Michael Shapiro, Olga Waupotitsch, Marjorie
323 Larson, Jim Westervelt : U.S. Army CERL, 1993. GRASS 4.1 Reference
324 Manual. U.S. Army Corps of Engineers, Construction Engineering Research
325 Laboratories, Champaign, Illinois, 1-425.
326
328 Documentation of related GRASS utilities :
329 http://grass.osgeo.org/grass64/manuals/html64_user/r.slope.aspect.html
331 http://grass.osgeo.org/grass64/manuals/html64_user/r.shaded.relief.html
333 http://grass.osgeo.org/grass64/manuals/html64_user/r.colors.html
335GDAL Wed Oct 3 2018 gdaldem(1)