Ubuntu Manpage: r.geomorphon - Calculates geomorphons (terrain forms) and associated geometry using machine vision

NAME

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

KEYWORDS

       raster, geomorphons, terrain patterns, machine vision geomorphometry

SYNOPSIS

       r.geomorphon
       r.geomorphon --help
       r.geomorphon [-me]  elevation=name   [forms=name]    [ternary=name]    [positive=name]    [negative=name]
       [intensity=name]       [exposition=name]       [range=name]       [variance=name]       [elongation=name]
       [azimuth=name]    [extend=name]    [width=name]   search=integer   skip=integer   flat=float   dist=float
       [prefix=string]   [step=float]   [start=float]   [--overwrite]  [--help]  [--verbose]  [--quiet]  [--ui]

   Flags:
       -m
           Use meters to define search units (default is cells)

       -e
           Use extended form correction

       --overwrite
           Allow output files to overwrite existing files

       --help
           Print usage summary

       --verbose
           Verbose module output

       --quiet
           Quiet module output

       --ui
           Force launching GUI dialog

   Parameters:
       elevation=name [required]
           Name of input elevation raster map

       forms=name
           Most common geomorphic forms

       ternary=name
           Code of ternary patterns

       positive=name
           Code of binary positive patterns

       negative=name
           Code of binary negative patterns

       intensity=name
           Rasters containing mean relative elevation of the form

       exposition=name
           Rasters containing maximum difference between extend and central cell

       range=name
           Rasters containing difference between max and min elevation of the form extend

       variance=name
           Rasters containing variance of form boundary

       elongation=name
           Rasters containing local elongation

       azimuth=name
           Rasters containing local azimuth of the elongation

       extend=name
           Rasters containing local extend (area) of the form

       width=name
           Rasters containing local width of the form

       search=integer [required]
           Outer search radius
           Default: 3

       skip=integer [required]
           Inner search radius
           Default: 0

       flat=float [required]
           Flatness threshold (degrees)
           Default: 1

       dist=float [required]
           Flatness distance, zero for none
           Default: 0

       prefix=string
           Prefix for maps resulting from multiresolution approach

       step=float
           Distance step for every iteration (zero to omit)
           Default: 0

       start=float
           Distance where search will start in multiple mode (zero to omit)
           Default: 0

DESCRIPTION

What is geomorphon:
Geomorphon is a new concept of presentation and analysis of terrain forms. This concept utilises 8-tuple
pattern of the visibility neighbourhood and breaks well known limitation of standard calculus approach
where all terrain forms cannot be detected in a single window size. The pattern arises from a comparison
of a focus pixel with its eight neighbors starting from the one located to the east and continuing
counterclockwise producing ternary operator. For example, a tuple {+,-,-,-,0,+,+,+} describes one
possible pattern of relative measures {higher, lower, lower, lower, equal, higher, higher, higher} for
pixels surrounding the focus pixel. It is important to stress that the visibility neighbors are not
necessarily an immediate neighbors of the focus pixel in the grid, but the pixels determined from the
line-of-sight principle along the eight principal directions. This principle relates surface relief and
horizontal distance by means of so-called zenith and nadir angles along the eight principal compass
directions. The ternary operator converts the information contained in all the pairs of zenith and nadir
angles into the ternary pattern (8-tuple). The result depends on the values of two parameters: search
radius (L) and relief threshold (d). The search radius is the maximum allowable distance for calculation
of zenith and nadir angles. The relief threshold is a minimum value of difference between LOSs angle
(zenith and nadir) that is considered significantly different from the horizon. Two lines-of-sight are
necessary due to zenith LOS only, does not detect positive forms correctly.

There are 3**8 = 6561 possible ternary patterns (8-tuples). However by eliminating all patterns that are
results of either rotation or reflection of other patterns wa set of 498 patterns remain referred as
geomorphons. This is a comprehensive and exhaustive set of idealized landforms that are independent of
the size, relief, and orientation of the actual landform.

Form recognition depends on two free parameters: Search radius and flatness threshold. Using larger
values of L and is tantamount to terrain classification from a higher and wider perspective, whereas
using smaller values of L and is tantamount to terrain classification from a local point of view. A
character of the map depends on the value of L. Using small value of L results in the map that correctly
identifies landforms if their size is smaller than L; landforms having larger sizes are broken down into
components. Using larger values of L allows simultaneous identification of landforms on variety of sizes
in expense of recognition smaller, second-order forms. There are two additional parameters: skip radius
used to eliminate impact of small irregularities. On the contrary flatness distance eliminates the impact
of very high distance (in meters) of search radius which may not detect elevation difference if this is
at very far distance. Important especially with low resolution DEMS.

OPTIONS

-m
All distance parameters (search, skip, flat distances) are supplied as meters instead of cells
(default). To avoid situation when supplied distances is smaller than one cell program first check if
supplied distance is longer than one cell in both NS and WE directions. For LatLong projection only
NS distance checked, because in latitude angular unit comprise always bigger or equal distance than
longitude one. If distance is supplied in cells, For all projections is recalculated into meters
according formula: number_of_cells*resolution_along_NS_direction. It is important if geomorphons are
calculated for large areas in LatLong projection.

elevation
Digital elevation model. Data can be of any type and any projection. During calculation DEM is stored
as floating point raster.

search
Determines length on the geodesic distances in all eight directions where line-of-sight is
calculated. To speed up calculation is determines only these cells which centers falls into the
distance.

skip
Determines length on the geodesic distances at the beginning of calculation all eight directions
where line-of-sight is yet calculated. To speed up calculation this distance is always recalculated
into number of cell which are skipped at the beginning of every line-of-sight and is equal in all
direction. This parameter eliminates forms of very small extend, smaller than skip parameter.

flat
The difference (in degrees) between zenith and nadir line-of-sight which indicate flat direction. If
higher threshold produce more flat maps. If resolution of the map is low (more than 1 km per cell)
threshold should be very small (much smaller than 1 degree) because on such distance 1 degree of
difference means several meters of high difference.

dist
>Flat distance. This is additional parameter defining the distance above which the threshold starts
to decrease to avoid problems with pseudo-flat line-of-sights if real elevation difference appears on
the distance where its value is higher (TO BE CORRECTED).

forms
Returns geomorphic map with 10 most popular terrestrial forms. Legend for forms, its definition by
the number of + and - and its idealized visualisation are presented at the image.

Forms represented by geomorphons:
ternary
returns code of one of 498 unique ternary patterns for every cell. The code is a decimal
representation of 8-tuple minimalised patterns written in ternary system. Full list of patterns is
available in source code directory as patterns.txt. This map can be used to create alternative form
classification using supervised approach.

positive and negative
returns codes binary patterns for zenith (positive) and nadir (negative) line of sights. The code is
a decimal representation of 8-tuple minimalised patterns written in binary system. Full list of
patterns is available in source code directory as patterns.txt.

NOTE: parameters below are very experimental. The usefulness of these parameters are currently under
investigation.

intensity
returns avarage difference between central cell of geomorphon and eight cells in visibility
neighbourhood. This parameter shows local (as is visible) exposition/abasement of the form in the
terrain.

range
returns difference between minimum and maximum values of visibility neighbourhood.

variance
returns variance (difference between particular values and mean value) of visibility neighbourhood.

extend
returns area of the polygon created by the 8 points where line-of-sight cuts the terrain (see image
in description section).

azimuth
returns orientation of the polygon constituting geomorphon. This orientation is currently calculated
as a orientation of least square fit line to the eight verticles of this polygon.

elongation
returns proportion between sides of the bounding box rectangle calculated for geomorphon rotated to
fit least square line.

width
returns length of the shorter side of the bounding box rectangle calculated for geomorphon rotated to
fit least square line.

NOTES

       From computational point of view there are no limitations of  input  DEM  and  free  parameters  used  in
       calculation.  However,  in  practice  there  are  some  issues  on  DEM resolution and search radius. Low
       resolution DEM especially above 1 km per cell requires smaller than default flatness  threshold.  On  the
       other  hand,  only forms with high local elevation difference will be detected correctly. It results from
       fact that on very high distance (of order  of  kilometers  or  higher)  even  relatively  high  elevation
       difference  will be recognized as flat. For example at the distance of 8 km (8 cells with 1 km resolution
       DEM) an relative elevation difference of at least 136 m is required to be noticed as  non-flat.  Flatness
       distance threshold may be helpful to avoid this problem.

EXAMPLES

   Geomorphon calculation: extraction of terrestrial landforms
       Geomorphon calculation example using the EU DEM 25m:
       g.region raster=eu_dem_25m -p
       r.geomorphon elevation=eu_dem_25m forms=eu_dem_25m_geomorph
       # verify terrestrial landforms found in DEM
       r.category eu_dem_25m_geomorph
        1  flat
        2  summit
        3  ridge
        4  shoulder
        5  spur
        6  slope
        7  hollow
        8  footslope
        9  valley
        10 depression

   Extraction of summits
       Using  the  resulting terrestrial landforms map, single landforms can be extracted, e.g. the summits, and
       converted into a vector point map:
       r.mapcalc expression="eu_dem_25m_summits = if(eu_dem_25m_geomorph == 2, 1, null())"
       r.thin input=eu_dem_25m_summits output=eu_dem_25m_summits_thinned
       r.to.vect input=eu_dem_25m_summits_thinned output=eu_dem_25m_summits type=point
       v.info input=eu_dem_25m_summits

REFERENCES

           •   Stepinski, T., Jasiewicz, J., 2011, Geomorphons - a new approach to classification  of  landform,
               in  :   Eds:  Hengl,  T., Evans, I.S., Wilson, J.P., and Gould, M., Proceedings of Geomorphometry
               2011,  Redlands, 109-112 (PDF)

           •   Jasiewicz,  J.,  Stepinski,  T.,   2013,  Geomorphons  -  a  pattern  recognition   approach   to
               classification   and   mapping   of   landforms,   Geomorphology,   vol.   182,   147-156   (DOI:
               10.1016/j.geomorph.2012.11.005)

AUTHORS

       Jarek Jasiewicz, Tomek Stepinski (merit contribution)

SOURCE CODE

       Available at: r.geomorphon source code (history)

       Accessed: unknown

       Main index | Raster index | Topics index | Keywords index | Graphical index | Full index

       © 2003-2022 GRASS Development Team, GRASS GIS 7.8.7 Reference Manual

GRASS 7.8.7                                                                                 r.geomorphon(1grass)