1r.geomorphon(1) GRASS GIS User's Manual r.geomorphon(1)
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6 r.geomorphon - Calculates geomorphons (terrain forms) and associated
7 geometry using machine vision approach.
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10 raster, geomorphons, terrain patterns, machine vision geomorphometry
11
13 r.geomorphon
14 r.geomorphon --help
15 r.geomorphon [-me] elevation=name [forms=name] [ternary=name]
16 [positive=name] [negative=name] [intensity=name] [exposi‐
17 tion=name] [range=name] [variance=name] [elongation=name]
18 [azimuth=name] [extend=name] [width=name] search=integer
19 skip=integer flat=float dist=float [prefix=string] [step=float]
20 [start=float] [--overwrite] [--help] [--verbose] [--quiet] [--ui]
21 Flags:
23 -m
24 Use meters to define search units (default is cells)
25 -e
27 Use extended form correction
28 --overwrite
30 Allow output files to overwrite existing files
31 --help
33 Print usage summary
34 --verbose
36 Verbose module output
37 --quiet
39 Quiet module output
40 --ui
42 Force launching GUI dialog
43 Parameters:
45 elevation=name [required]
46 Name of input elevation raster map
47 forms=name
49 Most common geomorphic forms
50 ternary=name
52 Code of ternary patterns
53 positive=name
55 Code of binary positive patterns
56 negative=name
58 Code of binary negative patterns
59 intensity=name
61 Rasters containing mean relative elevation of the form
62 exposition=name
64 Rasters containing maximum difference between extend and central
65 cell
66 range=name
68 Rasters containing difference between max and min elevation of the
69 form extend
70 variance=name
72 Rasters containing variance of form boundary
73 elongation=name
75 Rasters containing local elongation
76 azimuth=name
78 Rasters containing local azimuth of the elongation
79 extend=name
81 Rasters containing local extend (area) of the form
82 width=name
84 Rasters containing local width of the form
85 search=integer [required]
87 Outer search radius
88 Default: 3
89 skip=integer [required]
91 Inner search radius
92 Default: 0
93 flat=float [required]
95 Flatness threshold (degrees)
96 Default: 1
97 dist=float [required]
99 Flatness distance, zero for none
100 Default: 0
101 prefix=string
103 Prefix for maps resulting from multiresolution approach
104 step=float
106 Distance step for every iteration (zero to omit)
107 Default: 0
108 start=float
110 Distance where search will start in multiple mode (zero to omit)
111 Default: 0
112
114 What is geomorphon:
115 Geomorphon is a new concept of presentation and analysis of terrain
116 forms. This concept utilises 8-tuple pattern of the visibility neigh‐
117 bourhood and breaks well known limitation of standard calculus
118 approach where all terrain forms cannot be detected in a single window
119 size. The pattern arises from a comparison of a focus pixel with its
120 eight neighbors starting from the one located to the east and continu‐
121 ing counterclockwise producing ternary operator. For example, a tuple
122 {+,-,-,-,0,+,+,+} describes one possible pattern of relative measures
123 {higher, lower, lower, lower, equal, higher, higher, higher} for pixels
124 surrounding the focus pixel. It is important to stress that the visi‐
125 bility neighbors are not necessarily an immediate neighbors of the
126 focus pixel in the grid, but the pixels determined from the
127 line-of-sight principle along the eight principal directions. This
128 principle relates surface relief and horizontal distance by means of
129 so-called zenith and nadir angles along the eight principal compass
130 directions. The ternary operator converts the information contained in
131 all the pairs of zenith and nadir angles into the ternary pattern
132 (8-tuple). The result depends on the values of two parameters: search
133 radius (L) and relief threshold (d). The search radius is the maximum
134 allowable distance for calculation of zenith and nadir angles. The
135 relief threshold is a minimum value of difference between LOSs angle
136 (zenith and nadir) that is considered significantly different from the
137 horizon. Two lines-of-sight are necessary due to zenith LOS only, does
138 not detect positive forms correctly.
139 There are 3**8 = 6561 possible ternary patterns (8-tuples). However by
141 eliminating all patterns that are results of either rotation or reflec‐
142 tion of other patterns wa set of 498 patterns remain referred as geo‐
143 morphons. This is a comprehensive and exhaustive set of idealized
144 landforms that are independent of the size, relief, and orientation of
145 the actual landform.
146 Form recognition depends on two free parameters: Search radius and
148 flatness threshold. Using larger values of L and is tantamount to ter‐
149 rain classification from a higher and wider perspective, whereas using
150 smaller values of L and is tantamount to terrain classification from a
151 local point of view. A character of the map depends on the value of L.
152 Using small value of L results in the map that correctly identifies
153 landforms if their size is smaller than L; landforms having larger
154 sizes are broken down into components. Using larger values of L allows
155 simultaneous identification of landforms on variety of sizes in expense
156 of recognition smaller, second-order forms. There are two additional
157 parameters: skip radius used to eliminate impact of small irregulari‐
158 ties. On the contrary flatness distance eliminates the impact of very
159 high distance (in meters) of search radius which may not detect eleva‐
160 tion difference if this is at very far distance. Important especially
161 with low resolution DEMS.
162
164 -m
165 All distance parameters (search, skip, flat distances) are supplied
166 as meters instead of cells (default). To avoid situation when sup‐
167 plied distances is smaller than one cell program first check if
168 supplied distance is longer than one cell in both NS and WE direc‐
169 tions. For LatLong projection only NS distance checked, because in
170 latitude angular unit comprise always bigger or equal distance than
171 longitude one. If distance is supplied in cells, For all projec‐
172 tions is recalculated into meters according formula: num‐
173 ber_of_cells*resolution_along_NS_direction. It is important if geo‐
174 morphons are calculated for large areas in LatLong projection.
175 elevation
177 Digital elevation model. Data can be of any type and any projec‐
178 tion. During calculation DEM is stored as floating point raster.
179 search
181 Determines length on the geodesic distances in all eight directions
182 where line-of-sight is calculated. To speed up calculation is
183 determines only these cells which centers falls into the distance.
184 skip
186 Determines length on the geodesic distances at the beginning of
187 calculation all eight directions where line-of-sight is yet calcu‐
188 lated. To speed up calculation this distance is always recalculated
189 into number of cell which are skipped at the beginning of every
190 line-of-sight and is equal in all direction. This parameter elimi‐
191 nates forms of very small extend, smaller than skip parameter.
192 flat
194 The difference (in degrees) between zenith and nadir line-of-sight
195 which indicate flat direction. If higher threshold produce more
196 flat maps. If resolution of the map is low (more than 1 km per
197 cell) threshold should be very small (much smaller than 1 degree)
198 because on such distance 1 degree of difference means several
199 meters of high difference.
200 dist
202 >Flat distance. This is additional parameter defining the distance
203 above which the threshold starts to decrease to avoid problems with
204 pseudo-flat line-of-sights if real elevation difference appears on
205 the distance where its value is higher (TO BE CORRECTED).
206 forms
208 Returns geomorphic map with 10 most popular terrestrial forms. Leg‐
209 end for forms, its definition by the number of + and - and its ide‐
210 alized visualisation are presented at the image.
211 Forms represented by geomorphons:
213 ternary
214 returns code of one of 498 unique ternary patterns for every cell.
215 The code is a decimal representation of 8-tuple minimalised pat‐
216 terns written in ternary system. Full list of patterns is available
217 in source code directory as patterns.txt. This map can be used to
218 create alternative form classification using supervised approach.
219 positive and negative
221 returns codes binary patterns for zenith (positive) and nadir (neg‐
222 ative) line of sights. The code is a decimal representation of
223 8-tuple minimalised patterns written in binary system. Full list of
224 patterns is available in source code directory as patterns.txt.
225 NOTE: parameters below are very experimental. The usefulness of these
227 parameters are currently under investigation.
228 intensity
230 returns avarage difference between central cell of geomorphon and
231 eight cells in visibility neighbourhood. This parameter shows local
232 (as is visible) exposition/abasement of the form in the terrain.
233 range
235 returns difference between minimum and maximum values of visibility
236 neighbourhood.
237 variance
239 returns variance (difference between particular values and mean
240 value) of visibility neighbourhood.
241 extend
243 returns area of the polygon created by the 8 points where
244 line-of-sight cuts the terrain (see image in description section).
245 azimuth
247 returns orientation of the polygon constituting geomorphon. This
248 orientation is currently calculated as a orientation of least
249 square fit line to the eight verticles of this polygon.
250 elongation
252 returns proportion between sides of the bounding box rectangle cal‐
253 culated for geomorphon rotated to fit least square line.
254 width
256 returns length of the shorter side of the bounding box rectangle
257 calculated for geomorphon rotated to fit least square line.
258
260 From computational point of view there are no limitations of input DEM
261 and free parameters used in calculation. However, in practice there are
262 some issues on DEM resolution and search radius. Low resolution DEM
263 especially above 1 km per cell requires smaller than default flatness
264 threshold. On the other hand, only forms with high local elevation dif‐
265 ference will be detected correctly. It results from fact that on very
266 high distance (of order of kilometers or higher) even relatively high
267 elevation difference will be recognized as flat. For example at the
268 distance of 8 km (8 cells with 1 km resolution DEM) an relative eleva‐
269 tion difference of at least 136 m is required to be noticed as
270 non-flat. Flatness distance threshold may be helpful to avoid this
271 problem.
272
274 Geomorphon calculation: extraction of terrestrial landforms
275 Geomorphon calculation example using the EU DEM 25m:
276 g.region raster=eu_dem_25m -p
277 r.geomorphon elevation=eu_dem_25m forms=eu_dem_25m_geomorph
278 # verify terrestrial landforms found in DEM
279 r.category eu_dem_25m_geomorph
280 1 flat
281 2 summit
282 3 ridge
283 4 shoulder
284 5 spur
285 6 slope
286 7 hollow
287 8 footslope
288 9 valley
289 10 depression
290 Extraction of summits
292 Using the resulting terrestrial landforms map, single landforms can be
293 extracted, e.g. the summits, and converted into a vector point map:
294 r.mapcalc expression="eu_dem_25m_summits = if(eu_dem_25m_geomorph == 2, 1, null())"
295 r.thin input=eu_dem_25m_summits output=eu_dem_25m_summits_thinned
296 r.to.vect input=eu_dem_25m_summits_thinned output=eu_dem_25m_summits type=point
297 v.info input=eu_dem_25m_summits
298
300 r.param.scale
301
303 · Stepinski, T., Jasiewicz, J., 2011, Geomorphons - a new
304 approach to classification of landform, in : Eds: Hengl, T.,
305 Evans, I.S., Wilson, J.P., and Gould, M., Proceedings of Geo‐
306 morphometry 2011, Redlands, 109-112 (PDF)
307 · Jasiewicz, J., Stepinski, T., 2013, Geomorphons - a pattern
309 recognition approach to classification and mapping of land‐
310 forms, Geomorphology, vol. 182, 147-156 (DOI: 10.1016/j.geo‐
311 morph.2012.11.005)
312
314 Jarek Jasiewicz, Tomek Stepinski (merit contribution)
315
317 Available at: r.geomorphon source code (history)
318 Main index | Raster index | Topics index | Keywords index | Graphical
320 index | Full index
321 © 2003-2020 GRASS Development Team, GRASS GIS 7.8.5 Reference Manual
323GRASS 7.8.5 r.geomorphon(1)