1r.geomorphon(1)             GRASS GIS User's Manual            r.geomorphon(1)
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NAME

6       r.geomorphon   -  Calculates geomorphons (terrain forms) and associated
7       geometry using machine vision approach.
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KEYWORDS

10       raster, geomorphons, terrain patterns, machine vision geomorphometry
11

SYNOPSIS

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
22   Flags:
23       -m
24           Use meters to define search units (default is cells)
25
26       -e
27           Use extended form correction
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29       --overwrite
30           Allow output files to overwrite existing files
31
32       --help
33           Print usage summary
34
35       --verbose
36           Verbose module output
37
38       --quiet
39           Quiet module output
40
41       --ui
42           Force launching GUI dialog
43
44   Parameters:
45       elevation=name [required]
46           Name of input elevation raster map
47
48       forms=name
49           Most common geomorphic forms
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51       ternary=name
52           Code of ternary patterns
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54       positive=name
55           Code of binary positive patterns
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57       negative=name
58           Code of binary negative patterns
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60       intensity=name
61           Rasters containing mean relative elevation of the form
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63       exposition=name
64           Rasters  containing  maximum  difference between extend and central
65           cell
66
67       range=name
68           Rasters containing difference between max and min elevation of  the
69           form extend
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71       variance=name
72           Rasters containing variance of form boundary
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74       elongation=name
75           Rasters containing local elongation
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77       azimuth=name
78           Rasters containing local azimuth of the elongation
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80       extend=name
81           Rasters containing local extend (area) of the form
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83       width=name
84           Rasters containing local width of the form
85
86       search=integer [required]
87           Outer search radius
88           Default: 3
89
90       skip=integer [required]
91           Inner search radius
92           Default: 0
93
94       flat=float [required]
95           Flatness threshold (degrees)
96           Default: 1
97
98       dist=float [required]
99           Flatness distance, zero for none
100           Default: 0
101
102       prefix=string
103           Prefix for maps resulting from multiresolution approach
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105       step=float
106           Distance step for every iteration (zero to omit)
107           Default: 0
108
109       start=float
110           Distance where search will start in multiple mode (zero to omit)
111           Default: 0
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DESCRIPTION

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
140       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
147       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

OPTIONS

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.
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176       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.
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180       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
185       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.
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193       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.
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201       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
207       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
212   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.
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220       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
226       NOTE:  parameters  below are very experimental. The usefulness of these
227       parameters are currently under investigation.
228
229       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.
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234       range
235           returns difference between minimum and maximum values of visibility
236           neighbourhood.
237
238       variance
239           returns  variance  (difference  between  particular values and mean
240           value) of visibility neighbourhood.
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242       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
246       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
251       elongation
252           returns proportion between sides of the bounding box rectangle cal‐
253           culated for geomorphon rotated to fit least square line.
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255       width
256           returns length of the shorter side of the  bounding  box  rectangle
257           calculated for geomorphon rotated to fit least square line.
258

NOTES

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

EXAMPLES

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
291   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

SEE ALSO

300        r.param.scale
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REFERENCES

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
308           ·   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

AUTHORS

314       Jarek Jasiewicz, Tomek Stepinski (merit contribution)
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SOURCE CODE

317       Available at: r.geomorphon source code (history)
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319       Main  index  | Raster index | Topics index | Keywords index | Graphical
320       index | Full index
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322       © 2003-2020 GRASS Development Team, GRASS GIS 7.8.5 Reference Manual
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326GRASS 7.8.5                                                    r.geomorphon(1)
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