GRASS GIS manual: r.convergence

NAME

r.convergence

KEYWORDS

SYNOPSIS

r.convergence
r.convergence help
r.convergence [-cs] input=name output=name window=integer weights=string [--overwrite] [--verbose] [--quiet]

Flags:

-c: Use circular window (default: square)
-s: Add slope convergence (radically slow down calculation time)
--overwrite: Allow output files to overwrite existing files
--verbose: Verbose module output
--quiet: Quiet module output

Parameters:

input=name: Digital elevation model map
output=name: Output convergence index map
window=integer: Window size; Default: 3
weights=string: Method for reducing the impact of the cell due to distance; Options: standard,inverse,power,square,gentle; Default: standard

DESCRIPTION

Convergence index is a terrain parameter which show the structure of the relief as a set of convergent areas (channels) and divergent areas (ridges). It represents the agreement of aspect direction of surrounding cells with the teoretical matrix direction. Convergence index is mean (or weighted mean if weights are used) aspect difference between real aspect and theoretical maximum divergent direction matrix representing ideal peak (see figure) minus 90 degres. So if there is maximum agreement with divergent matrix the convergence index is (0 - 90) * 10/9 = -100. If there is ideal sink (maximum convergence) the convergence index is (180 -90) * 10/9 = 100. Slope and aspect ere calculated internaly with the same formula as in r.slope.aspect. Convergence index is very useful for analysis of lineaments especially represented by rigdes or chanell systems as well as valley recognition tool.

Figure: How convergence index is calculated (3 x 3 window)

REFERENCES

Claps, P., Fiorentino, M., Oliveto, G., (1994), Informational entropy of fractal river networks, Journal of Hydrology, 187(1-2), 145-156 .

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

Böhner J., Blaschke T., Montanarella, L. (eds.) (2008). SAGA Seconds Out. Hamburger Beiträge zur Physischen Geographie und Landschaftsökologie, 19:113

AUTHOR

Jarek Jasiewicz

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