Calculate the size of the local catchment area (contributing area), accumulated material, and flow path length, using top-down processing algorithms from the highest to the lowest cell.
Top-Down Processing is new with SAGA GIS 2.1.3. See rsaga.parallel.processing() with older versions.
rsaga.topdown.processing(
in.dem,
in.sinkroute,
in.weight,
in.mean,
in.material,
in.target,
in.lin.val,
in.lin.dir,
out.carea,
out.mean,
out.tot.mat,
out.acc.left,
out.acc.right,
out.flowpath,
step,
method = "mfd",
linear.threshold = Inf,
convergence = 1.1,
env = rsaga.env(),
...
)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 (the default) a character vector with the module's console output.
input: digital elevation model (DEM) as SAGA grid file (default file extension: .sgrd)
optional input: SAGA grid with sink routes
optional input: SAGA grid with weights
optional input: SAGA grid for mean over catchment calculation
optional input: SAGA grid with material
optional input: SAGA grid of accumulation target
optional input: SAGA grid providing values to be compared with linear flow threshold instead of catchment area
optional input: SAGA grid to be used for linear flow routing, if the value is a valid direction (0-7 = N, NE, E, SE, S, SW, W, NW)
output: catchment area grid
optional output: mean over catchment grid
optional output: total accumulated material grid
optional output: accumulated material from left side grid
optional output: accumulated material from right side grid
optional output: flow path length grid
integer >=1: step parameter
character or numeric: choice of processing algorithm (default "mfd", or 4):
0 Deterministic 8 ("d8" or 0)
1 Rho 8 ("rho8", or 1)
2 Braunschweiger Reliefmodell ("braunschweig" or 2)
3 Deterministic Infinity ("dinf" or 3)
4 Multiple Flow Direction ("mfd" or 4)
5 Multiple Triangular Flow Direction ("mtfd", or 5)
6 Multiple Maximum Gradient Based Flow Direction ("mdg", or 6)
numeric (number of grid cells): threshold above which linear flow (i.e. the Deterministic 8 algorithm) will be used; linear flow is disabled for linear.threshold=Inf (the default)
numeric >=0: a parameter for tuning convergent/ divergent flow; default value of 1.1 gives realistic results and should not be changed
list, setting up a SAGA geoprocessing environment as created by rsaga.env()
further arguments to rsaga.geoprocessor()
Alexander Brenning and Donovan Bangs (R interface), Olaf Conrad (SAGA module), Thomas Grabs (MTFD algorithm)
Refer to the references for details on the available algorithms.
Deterministic 8:
O'Callaghan, J.F., Mark, D.M. (1984): The extraction of drainage networks from digital elevation data. Computer Vision, Graphics and Image Processing, 28: 323-344.
Rho 8:
Fairfield, J., Leymarie, P. (1991): Drainage networks from grid digital elevation models. Water Resources Research, 27: 709-717.
Braunschweiger Reliefmodell:
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 zu Analyse von Agrar-Oekosystemen, eds.: Bork, H.-R., Rohdenburg, H., p. 1-15.
Deterministic Infinity:
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.
Multiple Flow Direction:
Freeman, G.T. (1991): Calculating catchment area with divergent flow based on a regular grid. Computers and Geosciences, 17: 413-22.
Quinn, P.F., Beven, K.J., Chevallier, P., Planchon, O. (1991): The prediction of hillslope flow paths for distributed hydrological modelling using digital terrain models. Hydrological Processes, 5: 59-79.
Multiple Triangular Flow Direction:
Seibert, J., McGlynn, B. (2007): A new triangular multiple flow direction algorithm for computing upslope areas from gridded digital elevation models. Water Ressources Research, 43, W04501.
Multiple Flow Direction Based on Maximum Downslope Gradient:
Qin, C.Z., Zhu, A-X., Pei, T., Li, B.L., Scholten, T., Zhou, C.H. (2011): An approach to computing topographic wetness index based on maximum downslope gradient. Precision Agriculture, 12(1): 32-43.
rsaga.parallel.processing(), rsaga.wetness.index(), rsaga.geoprocessor(), rsaga.env()
if (FALSE) {
# Calculation of contributing area with default settings:
rsaga.topdown.processing(in.dem = "dem", out.carea = "carea")
# Calculation of contributing area by maximunm downslope gradient:
rsaga.topdown.processing(in.dem = "dem", out.carea = "carea",
method = "mdg")
}
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