Parallel Processing

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Description

Calculate the size of the local catchment area (contributing area), the catchment height, catchment slope and aspect, and flow path length, using parallel processing algorithms including the recommended multiple flow direction algorithm. This set of algorithms processes a digital elevation model (DEM) downwards from the highest to the lowest cell.
No longer supported with SAGA GIS 2.1.3+. See rsaga.topdown.processing.

Usage

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rsaga.parallel.processing(in.dem, in.sinkroute, in.weight, out.carea,
  out.cheight, out.cslope, out.caspect, out.flowpath, step, method = "mfd",
  linear.threshold = Inf, convergence = 1.1, env = rsaga.env(), ...)

Arguments

in.dem

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

in.sinkroute

optional input: SAGA grid with sink routes

in.weight

optional intput: SAGA grid with weights

out.carea

output: catchment area grid

out.cheight

optional output: catchment height grid

out.cslope

optional output: catchment slope grid

out.caspect

optional output: catchment aspect grid

out.flowpath

optional output: flow path length grid

step

integer >=1: step parameter

method

character or numeric: choice of processing algorithm: Deterministic 8 ("d8" or 0), Rho 8 ("rho8" or 1), Braunschweiger Reliefmodell ("braunschweig" or 2), Deterministic Infinity ("dinf" or 3), Multiple Flow Direction ("mfd" or 4, the default), Multiple Triangular Flow Direction ("mtfd", or 5).

linear.threshold

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)

convergence

numeric >=0: a parameter for tuning convergent/ divergent flow; default value of 1.1 gives realistic results and should not be changed

env

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

...

further arguments to rsaga.geoprocessor

Details

Refer to the references for details on the available algorithms.

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 (the default) a character vector with the module's console output.

Note

This function uses module Parallel Processing (version 2.0.7+: Catchment Area (Parallel) from SAGA library ta_hydrology.

The SAGA GIS 2.0.6+ version of the module adds more (optional) input and output grids that are currently not supported by this wrapper function. Use rsaga.geoprocessor for access to these options, and see rsaga.get.usage("ta_hydrology","Catchment Area (Parallel)") for information on new arguments.

Author(s)

Alexander Brenning (R interface), Olaf Conrad (SAGA module), Thomas Grabs (MTFD algorithm)

References

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.

See Also

rsaga.topdown.processing, rsaga.wetness.index, rsaga.geoprocessor, rsaga.env

Examples

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## Not run: 
# SAGA GIS 2.0.6+:
rsaga.get.usage("ta_hydrology","Catchment Area (Parallel)")
# earlier versions of SAGA GIS:
#rsaga.get.usage("ta_hydrology","Parallel Processing")
# execute model with typical settings:
rsaga.parallel.processing(in.dem = "dem", out.carea = "carea", out.cslope = "cslope")
# cslope is in radians - convert to degree:
fac = round(180/pi, 4)
formula = paste(fac, "*a", sep = "")
rsaga.grid.calculus("cslope", "cslopedeg", formula)

## End(Not run)

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