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 | -igor]
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 -igor:
169 (starting with GDAL 3.0) shading which tries to minimize effects on
170 other map features beneath. Can't be used with -alt option.
171 Multidirectional hillshading applies the formula of
173 http://pubs.usgs.gov/of/1992/of92-422/of92-422.pdf.
174 Igor's hillshading uses formula from Maperitive
176 http://maperitive.net/docs/Commands/GenerateReliefImageIgor.html.
177 slope
179 This command will take a DEM raster and output a 32-bit float raster
180 with slope values. You have the option of specifying the type of slope
181 value you want: degrees or percent slope. In cases where the horizontal
182 units differ from the vertical units, you can also supply a scaling
183 factor.
184 The value -9999 is used as the output nodata value.
186 The following specific options are available :
188 -p :
190 if specified, the slope will be expressed as percent slope.
191 Otherwise, it is expressed as degrees
192 -s scale:
194 ratio of vertical units to horizontal. If the horizontal unit of
195 the source DEM is degrees (e.g Lat/Long WGS84 projection), you can
196 use scale=111120 if the vertical units are meters (or scale=370400
197 if they are in feet)
198 aspect
200 This command outputs a 32-bit float raster with values between 0° and
201 360° representing the azimuth that slopes are facing. The definition of
202 the azimuth is such that : 0° means that the slope is facing the North,
203 90° it's facing the East, 180° it's facing the South and 270° it's
204 facing the West (provided that the top of your input raster is north
205 oriented). The aspect value -9999 is used as the nodata value to
206 indicate undefined aspect in flat areas with slope=0.
207 The following specifics options are available :
209 -trigonometric:
211 return trigonometric angle instead of azimuth. Thus 0° means East,
212 90° North, 180° West, 270° South
213 -zero_for_flat:
215 return 0 for flat areas with slope=0, instead of -9999
216 By using those 2 options, the aspect returned by gdaldem aspect should
218 be identical to the one of GRASS r.slope.aspect. Otherwise, it's
219 identical to the one of Matthew Perry's aspect.cpp utility.
220 color-relief
222 This command outputs a 3-band (RGB) or 4-band (RGBA) raster with values
223 are computed from the elevation and a text-based color configuration
224 file, containing the association between various elevation values and
225 the corresponding wished color. By default, the colors between the
226 given elevation values are blended smoothly and the result is a nice
227 colorized DEM. The -exact_color_entry or -nearest_color_entry options
228 can be used to avoid that linear interpolation for values that don't
229 match an index of the color configuration file.
230 The following specifics options are available :
232 color_text_file:
234 text-based color configuration file
235 -alpha :
237 add an alpha channel to the output raster
238 -exact_color_entry :
240 use strict matching when searching in the color configuration file.
241 If none matching color entry is found, the '0,0,0,0' RGBA
242 quadruplet will be used
243 -nearest_color_entry :
245 use the RGBA quadruplet corresponding to the closest entry in the
246 color configuration file.
247 The color-relief mode is the only mode that supports VRT as output
249 format. In that case, it will translate the color configuration file
250 into appropriate LUT elements. Note that elevations specified as
251 percentage will be translated as absolute values, which must be taken
252 into account when the statistics of the source raster differ from the
253 one that was used when building the VRT.
254 The text-based color configuration file generally contains 4 columns
256 per line : the elevation value and the corresponding Red, Green, Blue
257 component (between 0 and 255). The elevation value can be any floating
258 point value, or the nv keyword for the nodata value.. The elevation can
259 also be expressed as a percentage : 0% being the minimum value found in
260 the raster, 100% the maximum value.
261 An extra column can be optionally added for the alpha component. If it
263 is not specified, full opacity (255) is assumed.
264 Various field separators are accepted : comma, tabulation, spaces, ':'.
266 Common colors used by GRASS can also be specified by using their name,
268 instead of the RGB triplet. The supported list is : white, black, red,
269 green, blue, yellow, magenta, cyan, aqua, grey/gray, orange, brown,
270 purple/violet and indigo.
271 Since GDAL 1.8.0, GMT .cpt palette files are also supported
273 (COLOR_MODEL = RGB only).
274 Note: the syntax of the color configuration file is derived from the
276 one supported by GRASS r.colors utility. ESRI HDR color table files
277 (.clr) also match that syntax. The alpha component and the support of
278 tab and comma as separators are GDAL specific extensions.
279 For example :
281 3500 white
283 2500 235:220:175
284 50% 190 185 135
285 700 240 250 150
286 0 50 180 50
287 nv 0 0 0 0
288 TRI
291 This command outputs a single-band raster with values computed from the
292 elevation. TRI stands for Terrain Ruggedness Index, which is defined as
293 the mean difference between a central pixel and its surrounding cells
294 (see Wilson et al 2007, Marine Geodesy 30:3-35).
295 The value -9999 is used as the output nodata value.
297 There are no specific options.
299 TPI
301 This command outputs a single-band raster with values computed from the
302 elevation. TPI stands for Topographic Position Index, which is defined
303 as the difference between a central pixel and the mean of its
304 surrounding cells (see Wilson et al 2007, Marine Geodesy 30:3-35).
305 The value -9999 is used as the output nodata value.
307 There are no specific options.
309 roughness
311 This command outputs a single-band raster with values computed from the
312 elevation. Roughness is the largest inter-cell difference of a central
313 pixel and its surrounding cell, as defined in Wilson et al (2007,
314 Marine Geodesy 30:3-35).
315 The value -9999 is used as the output nodata value.
317 There are no specific options.
319
321 Starting with GDAL 2.1, this utility is also callable from C with
322 GDALDEMProcessing().
323
325 Matthew Perry perrygeo@gmail.com, Even Rouault even.rouault@mines-
326 paris.org, Howard Butler hobu.inc@gmail.com, Chris Yesson
327 chris.yesson@ioz.ac.uk
328 Derived from code by Michael Shapiro, Olga Waupotitsch, Marjorie
330 Larson, Jim Westervelt : U.S. Army CERL, 1993. GRASS 4.1 Reference
331 Manual. U.S. Army Corps of Engineers, Construction Engineering Research
332 Laboratories, Champaign, Illinois, 1-425.
333
335 Documentation of related GRASS utilities :
336 http://grass.osgeo.org/grass64/manuals/html64_user/r.slope.aspect.html
338 http://grass.osgeo.org/grass64/manuals/html64_user/r.shaded.relief.html
340 http://grass.osgeo.org/grass64/manuals/html64_user/r.colors.html
342GDAL Tue Mar 3 2020 gdaldem(1)