1GDALDEM(1) GDAL GDALDEM(1)
2
6 gdaldem - Tools to analyze and visualize DEMs.
7
9 gdaldem <mode> <input> <output> <options>
10 Generate a shaded relief map from any GDAL-supported elevation raster:
12 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 [-alg ZevenbergenThorne] [-combined | -multidirectional | -igor]
17 [-compute_edges] [-b Band (default=1)] [-of format] [-co "NAME=VALUE"]* [-q]
18 Generate a slope map from any GDAL-supported elevation raster:
20 gdaldem slope input_dem output_slope_map
22 [-p use percent slope (default=degrees)] [-s scale* (default=1)]
23 [-alg ZevenbergenThorne]
24 [-compute_edges] [-b Band (default=1)] [-of format] [-co "NAME=VALUE"]* [-q]
25 Generate an aspect map from any GDAL-supported elevation raster, out‐
27 puts a 32-bit float raster with pixel values from 0-360 indicating az‐
28 imuth:
29 gdaldem aspect input_dem output_aspect_map
31 [-trigonometric] [-zero_for_flat]
32 [-alg ZevenbergenThorne]
33 [-compute_edges] [-b Band (default=1)] [-of format] [-co "NAME=VALUE"]* [-q]
34 Generate a color relief map from any GDAL-supported elevation raster:
36 gdaldem color-relief input_dem color_text_file output_color_relief_map
38 [-alpha] [-exact_color_entry | -nearest_color_entry]
39 [-b Band (default=1)] [-of format] [-co "NAME=VALUE"]* [-q]
40 where color_text_file contains lines of the format "elevation_value red green blue"
41 Generate a Terrain Ruggedness Index (TRI) map from any GDAL-supported
43 elevation raster:
44 gdaldem TRI input_dem output_TRI_map
46 [-compute_edges] [-b Band (default=1)] [-of format] [-q]
47 Generate a Topographic Position Index (TPI) map from any GDAL-supported
49 elevation raster:
50 gdaldem TPI input_dem output_TPI_map
52 [-compute_edges] [-b Band (default=1)] [-of format] [-q]
53 Generate a roughness map from any GDAL-supported elevation raster:
55 gdaldem roughness input_dem output_roughness_map
57 [-compute_edges] [-b Band (default=1)] [-of format] [-q]
58
60 The gdaldem generally assumes that x, y and z units are identical. If
61 x (east-west) and y (north-south) units are identical, but z (eleva‐
62 tion) units are different, the scale (-s) option can be used to set the
63 ratio of vertical units to horizontal. For LatLong projections near
64 the equator, where units of latitude and units of longitude are simi‐
65 lar, elevation (z) units can be converted to be compatible by using
66 scale=370400 (if elevation is in feet) or scale=111120 (if elevation is
67 in meters). For locations not near the equator, it would be best to
68 reproject your grid using gdalwarp before using gdaldem.
69 <mode> Where <mode> is one of the seven available modes:
71 • hillshade
73 Generate a shaded relief map from any GDAL-supported eleva‐
74 tion raster
75 • slope
77 Generate a slope map from any GDAL-supported elevation
78 raster aspect to generate an aspect map from any GDAL-sup‐
79 ported elevation raster
80 • color-relief
82 Generate a color relief map from any GDAL-supported eleva‐
83 tion raster.
84 • TRI
86 Generate a map of Terrain Ruggedness Index from any
87 GDAL-supported elevation raster.
88 • TPI
90 Generate a map of Topographic Position Index from any
91 GDAL-supported elevation raster.
92 • roughness
94 Generate a map of roughness from any GDAL-supported eleva‐
95 tion raster.
96 The following general options are available:
98 input_dem
100 The input DEM raster to be processed
101 output_xxx_map
103 The output raster produced
104 -of <format>
106 Select the output format.
107 New in version 2.3.0: If not specified, the format is guessed
109 from the extension (previously was raster.gtiff). Use the short
110 format name.
111 -compute_edges
114 Do the computation at raster edges and near nodata values
115 alg ZevenbergenThorne
117 Use Zevenbergen & Thorne formula, instead of Horn's formula, to
118 compute slope & aspect. The literature suggests Zevenbergen &
119 Thorne to be more suited to smooth landscapes, whereas Horn's
120 formula to perform better on rougher terrain.
121 -b <band>
123 Select an input band to be processed. Bands are numbered from 1.
124 -co <NAME=VALUE>
126 Many formats have one or more optional creation options that can
127 be used to control particulars about the file created. For in‐
128 stance, the GeoTIFF driver supports creation options to control
129 compression, and whether the file should be tiled.
130 The creation options available vary by format driver, and some
132 simple formats have no creation options at all. A list of op‐
133 tions supported for a format can be listed with the --formats
134 command line option but the documentation for the format is the
135 definitive source of information on driver creation options.
136 See raster_drivers format specific documentation for legal cre‐
137 ation options for each format.
138 -q Suppress progress monitor and other non-error output.
140 For all algorithms, except color-relief, a nodata value in the target
142 dataset will be emitted if at least one pixel set to the nodata value
143 is found in the 3x3 window centered around each source pixel. The con‐
144 sequence is that there will be a 1-pixel border around each image set
145 with nodata value.
146 If -compute_edges is specified, gdaldem will compute values at image
147 edges or if a nodata value is found in the 3x3 window, by interpo‐
148 lating missing values.
149
151 hillshade
152 This command outputs an 8-bit raster with a nice shaded relief effect.
153 It’s very useful for visualizing the terrain. You can optionally spec‐
154 ify the azimuth and altitude of the light source, a vertical exaggera‐
155 tion factor and a scaling factor to account for differences between
156 vertical and horizontal units.
157 The value 0 is used as the output nodata value.
159 The following specific options are available :
161 -z <factor>
163 Vertical exaggeration used to pre-multiply the elevations
164 -s <scale>
166 Ratio of vertical units to horizontal. If the horizontal unit of
167 the source DEM is degrees (e.g Lat/Long WGS84 projection), you
168 can use scale=111120 if the vertical units are meters (or
169 scale=370400 if they are in feet)
170 -az <azimuth>
172 Azimuth of the light, in degrees. 0 if it comes from the top of
173 the raster, 90 from the east, ... The default value, 315, should
174 rarely be changed as it is the value generally used to generate
175 shaded maps.
176 -alt <altitude>
178 Altitude of the light, in degrees. 90 if the light comes from
179 above the DEM, 0 if it is raking light.
180 -combined
182 combined shading, a combination of slope and oblique shading.
183 -multidirectional
185 multidirectional shading, a combination of hillshading illumi‐
186 nated from 225 deg, 270 deg, 315 deg, and 360 deg azimuth.
187 New in version 2.2.
189 -igor shading which tries to minimize effects on other map features
192 beneath. Can't be used with -alt option.
193 New in version 3.0.
195 Multidirectional hillshading applies the formula of
198 http://pubs.usgs.gov/of/1992/of92-422/of92-422.pdf.
199 Igor's hillshading uses formula from Maperitive
201 http://maperitive.net/docs/Commands/GenerateReliefImageIgor.html.
202 slope
204 This command will take a DEM raster and output a 32-bit float raster
205 with slope values. You have the option of specifying the type of slope
206 value you want: degrees or percent slope. In cases where the horizontal
207 units differ from the vertical units, you can also supply a scaling
208 factor.
209 The value -9999 is used as the output nodata value.
211 The following specific options are available :
213 -p If specified, the slope will be expressed as percent slope. Oth‐
215 erwise, it is expressed as degrees
216 -s
218 Ratio of vertical units to horizontal. If the horizontal unit of the
219 source DEM is degrees (e.g Lat/Long WGS84 projection), you can use
220 scale=111120 if the vertical units are meters (or scale=370400 if
221 they are in feet).
222 aspect
224 This command outputs a 32-bit float raster with values between 0° and
225 360° representing the azimuth that slopes are facing. The definition of
226 the azimuth is such that : 0° means that the slope is facing the North,
227 90° it's facing the East, 180° it's facing the South and 270° it's fac‐
228 ing the West (provided that the top of your input raster is north ori‐
229 ented). The aspect value -9999 is used as the nodata value to indicate
230 undefined aspect in flat areas with slope=0.
231 The following specifics options are available :
233 -trigonometric
235 Return trigonometric angle instead of azimuth. Thus 0° means
236 East, 90° North, 180° West, 270° South.
237 -zero_for_flat
239 Return 0 for flat areas with slope=0, instead of -9999.
240 By using those 2 options, the aspect returned by gdaldem aspect should
242 be identical to the one of GRASS r.slope.aspect. Otherwise, it's iden‐
243 tical to the one of Matthew Perry's aspect.cpp utility.
244 color-relief
246 This command outputs a 3-band (RGB) or 4-band (RGBA) raster with values
247 are computed from the elevation and a text-based color configuration
248 file, containing the association between various elevation values and
249 the corresponding wished color. By default, the colors between the
250 given elevation values are blended smoothly and the result is a nice
251 colorized DEM. The -exact_color_entry or -nearest_color_entry options
252 can be used to avoid that linear interpolation for values that don't
253 match an index of the color configuration file.
254 The following specifics options are available :
256 color_text_file
258 Text-based color configuration file
259 -alpha Add an alpha channel to the output raster
261 -exact_color_entry
263 Use strict matching when searching in the color configuration
264 file. If none matching color entry is found, the "0,0,0,0" RGBA
265 quadruplet will be used
266 -nearest_color_entry
268 Use the RGBA quadruplet corresponding to the closest entry in
269 the color configuration file.
270 The color-relief mode is the only mode that supports VRT as output for‐
272 mat. In that case, it will translate the color configuration file into
273 appropriate LUT elements. Note that elevations specified as percentage
274 will be translated as absolute values, which must be taken into account
275 when the statistics of the source raster differ from the one that was
276 used when building the VRT.
277 The text-based color configuration file generally contains 4 columns
279 per line: the elevation value and the corresponding Red, Green, Blue
280 component (between 0 and 255). The elevation value can be any floating
281 point value, or the nv keyword for the nodata value. The elevation can
282 also be expressed as a percentage: 0% being the minimum value found in
283 the raster, 100% the maximum value.
284 An extra column can be optionally added for the alpha component. If it
286 is not specified, full opacity (255) is assumed.
287 Various field separators are accepted: comma, tabulation, spaces, ':'.
289 Common colors used by GRASS can also be specified by using their name,
291 instead of the RGB triplet. The supported list is: white, black, red,
292 green, blue, yellow, magenta, cyan, aqua, grey/gray, orange, brown,
293 purple/violet and indigo.
294 GMT .cpt palette files are also supported (COLOR_MODEL = RGB only).
295 Note: the syntax of the color configuration file is derived from the
297 one supported by GRASS r.colors utility. ESRI HDR color table files
298 (.clr) also match that syntax. The alpha component and the support of
299 tab and comma as separators are GDAL specific extensions.
300 For example :
302 3500 white
304 2500 235:220:175
305 50% 190 185 135
306 700 240 250 150
307 0 50 180 50
308 nv 0 0 0 0
309 To implement a "round to the floor value" mode, the elevation value can
311 be duplicate with a new value being slightly above the threshold. For
312 example to have red in [0,10], green in ]10,20] and blue in ]20,30]:
313 :: 0 red 10 red 10.001 green 20 green 20.001 blue
315 30 blue
316 TRI
318 This command outputs a single-band raster with values computed from the
319 elevation. TRI stands for Terrain Ruggedness Index, which is defined
320 as the mean difference between a central pixel and its surrounding
321 cells (see Wilson et al 2007, Marine Geodesy 30:3-35).
322 The value -9999 is used as the output nodata value.
324 There are no specific options.
326 TPI
328 This command outputs a single-band raster with values computed from the
329 elevation. TPI stands for Topographic Position Index, which is defined
330 as the difference between a central pixel and the mean of its surround‐
331 ing cells (see Wilson et al 2007, Marine Geodesy 30:3-35).
332 The value -9999 is used as the output nodata value.
334 There are no specific options.
336 roughness
338 This command outputs a single-band raster with values computed from the
339 elevation. Roughness is the largest inter-cell difference of a central
340 pixel and its surrounding cell, as defined in Wilson et al (2007, Ma‐
341 rine Geodesy 30:3-35).
342 The value -9999 is used as the output nodata value.
344 There are no specific options.
346
348 This utility is also callable from C with GDALDEMProcessing().
349 New in version 2.1.
351
354 Matthew Perry perrygeo@gmail.com, Even Rouault
355 even.rouault@spatialys.com, Howard Butler hobu.inc@gmail.com, Chris
356 Yesson chris.yesson@ioz.ac.uk
357 Derived from code by Michael Shapiro, Olga Waupotitsch, Marjorie Lar‐
359 son, Jim Westervelt: U.S. Army CERL, 1993. GRASS 4.1 Reference Manual.
360 U.S. Army Corps of Engineers, Construction Engineering Research Labora‐
361 tories, Champaign, Illinois, 1-425.
362
364 Documentation of related GRASS utilities:
365 http://grass.osgeo.org/grass64/manuals/html64_user/r.slope.aspect.html
367 http://grass.osgeo.org/grass64/manuals/html64_user/r.shaded.relief.html
369 http://grass.osgeo.org/grass64/manuals/html64_user/r.colors.html
371
373 Matthew Perry <perrygeo@gmail.com>, Even Rouault <even.rouault@spa‐
374 tialys.com>, Howard Butler <hobu.inc@gmail.com>, Chris Yesson
375 <chris.yesson@ioz.ac.uk>
376
378 1998-2021
379 Mar 24, 2021 GDALDEM(1)