Slope, Aspect, Curvature

Description

Calculates local morphometric terrain attributes (i.e. slope, aspect, and curvatures). Intended for use with SAGA v 2.1.1+. For older versions use rsaga.local.morphometry.

Usage

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rsaga.slope.asp.curv(in.dem, out.slope, out.aspect, out.cgene, out.cprof,
  out.cplan, out.ctang, out.clong, out.ccros, out.cmini, out.cmaxi, out.ctota,
  out.croto, method = "poly2zevenbergen", unit.slope = "radians",
  unit.aspect = "radians", env = rsaga.env(), ...)

Arguments

in.dem

input: digital elevation model as SAGA grid file (.sgrd)

out.slope

optional output: slope

out.aspect

optional output: aspect

out.cgene

optional output: general curvature

out.cprof

optional output: profile curvature (vertical curvature; degrees)

out.cplan

optional output: plan curvature (horizontal curvature; degrees)

out.ctang

optional output: tangential curvature (degrees)

out.clong

optional output: longitudinal curvature (degrees) Zevenbergen & Thorne (1987) refer to this as profile curvature

out.ccros

optional output: cross-sectional curvature (degrees) Zevenbergen & Thorne (1987) refer to this as the plan curvature

out.cmini

optional output: minimal curvature (degrees)

out.cmaxi

optional output: maximal curvature (degrees)

out.ctota

optional output: total curvature (degrees)

out.croto

optional output: flow line curvature (degrees)

method

character algorithm (see References):

  • [0] Maximum Slope - Travis et al. (1975) ("maxslope")

  • [1] Max. Triangle Slope - Tarboton (1997) ("maxtriangleslope")

  • [2] Least Squares Fit Plane - Costa-Cabral & Burgess (1996) ("lsqfitplane")

  • [3] Fit 2nd Degree Polynomial - Evans (1979) ("poly2evans")

  • [4] Fit 2nd Degree Polynomial - Heerdegen and Beran (1982) ("poly2heerdegen")

  • [5] Fit 2nd Degree Polynomial - Bauer et al. (1985) ("poly2bauer")

  • [6] default: Fit 2nd Degree Polynomial - Zevenbergen & Thorne (1987) ("poly2zevenbergen")

  • [7] Fit 3rd Degree Polynomial - Haralick (1983) ("poly3haralick")

unit.slope

character or numeric (default "radians"):

  • [0] "radians"

  • [1] "degrees"

  • [2] "percent"

unit.aspect

character or numeric (default is 0, or "radians"):

  • [0] "radians"

  • [1] "degrees"

env

list, setting up a SAGA geoprocessing environment as created by rsaga.env

...

further arguments to rsaga.geoprocessor

Details

Profile and plan curvature calculation (out.cprof, out.cplan) changed in SAGA GIS 2.1.1+ compared to earlier versions. See the following thread on sourceforge.net for an ongoing discussion: http://sourceforge.net/p/saga-gis/discussion/354013/thread/e9d07075/#5727

Value

The type of object returned depends on the intern argument passed to the rsaga.geoprocessor. For intern=FALSE it is a numerical error code (0: success), or otherwise (default) a character vector with the module's console output.

Author(s)

Alexander Brenning and Donovan Bangs (R interface), Olaf Conrad (SAGA module)

References

General references:

Jones KH (1998) A comparison of algorithms used to compute hill slope as a property of the DEM. Computers and Geosciences. 24 (4): 315-323.

References on specific methods:

Maximum Slope:

Travis, M.R., Elsner, G.H., Iverson, W.D., Johnson, C.G. (1975): VIEWIT: computation of seen areas, slope, and aspect for land-use planning. USDA F.S. Gen. Tech. Rep. PSW-11/1975, 70 p. Berkeley, California, U.S.A.

Maximum Triangle Slope:

Tarboton, D.G. (1997): A new method for the determination of flow directions and upslope areas in grid digital elevation models. Water Ressources Research, 33(2): 309-319.

Least Squares or Best Fit Plane:

Beasley, D.B., Huggins, L.F. (1982): ANSWERS: User's manual. U.S. EPA-905/9-82-001, Chicago, IL, 54 pp.

Costa-Cabral, M., Burges, S.J. (1994): Digital Elevation Model Networks (DEMON): a model of flow over hillslopes for computation of contributing and dispersal areas. Water Resources Research, 30(6): 1681-1692.

Fit 2nd Degree Polynomial:

Evans, I.S. (1979): An integrated system of terrain analysis and slope mapping. Final Report on grant DA-ERO-591-73-G0040. University of Durham, England.

Bauer, J., Rohdenburg, H., Bork, H.-R. (1985): Ein Digitales Reliefmodell als Vorraussetzung fuer ein deterministisches Modell der Wasser- und Stoff-Fluesse. Landschaftsgenese und Landschaftsoekologie, H. 10, Parameteraufbereitung fuer deterministische Gebiets-Wassermodelle, Grundlagenarbeiten zur Analyse von Agrar-Oekosystemen, eds.: Bork, H.-R., Rohdenburg, H., p. 1-15.

Heerdegen, R.G., Beran, M.A. (1982): Quantifying source areas through land surface curvature. Journal of Hydrology, 57.

Zevenbergen, L.W., Thorne, C.R. (1987): Quantitative analysis of land surface topography. Earth Surface Processes and Landforms, 12: 47-56.

Fit 3.Degree Polynomial:

Haralick, R.M. (1983): Ridge and valley detection on digital images. Computer Vision, Graphics and Image Processing, 22(1): 28-38.

For a discussion on the calculation of slope by ArcGIS check these links:

http://forums.esri.com/Thread.asp?c=93&f=1734&t=239914

http://webhelp.esri.com/arcgisdesktop/9.2/index.cfm?topicname=how_slope_works

See Also

rsaga.local.morphometry, rsaga.parallel.processing, rsaga.geoprocessor, rsaga.env

Examples

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## Not run: 
# Simple slope, aspect, and general curvature in degrees:
rsaga.slope.asp.curv("lican.sgrd", "slope", "aspect", "curvature",
                     method = "maxslope", unit.slope = "degrees", unit.aspect = "degrees")
# same for ASCII grids (default extension .asc):
rsaga.esri.wrapper(rsaga.slope.asp.curv,
                   in.dem="lican", out.slope="slope",
                   out.aspect = "aspect", out.cgene = "curvature",
                   method="maxslope", unit.slope = "degrees", unit.aspect = "degrees")

## End(Not run)

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