r.windfetch - GRASS GIS manual

Note: This document is for an older version of GRASS GIS that has been discontinued. You should upgrade, and read the current manual page.

NAME

r.windfetch - Computes wind fetch which is the length of water over which winds blow without obstruction

KEYWORDS

raster, distance, wind

SYNOPSIS

r.windfetch

r.windfetch --help

r.windfetch input=name [coordinates=east,north[,east,north,...]] [points=name] step=integer direction=integer minor_directions=integer minor_step=integer [output_file=name] [format=string] [--overwrite] [--help] [--verbose] [--quiet] [--ui]

Flags:

--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:

input=name [required]: Name of input land/water land use map; Binary input where 1 is land and 0 is water
coordinates=east,north[,east,north,...]: Coordinates for which to compute wind fetch
points=name: Name of vector points map for fetch computation; Or data source for direct OGR access
step=integer [required]: Angular step at which to compute wind fetch (0 is East, counterclockwise); Options: 0-360; Default: 15
direction=integer [required]: Direction at which to start calculating fetch.; Options: 0-359; Default: 0
minor_directions=integer [required]: Number of minor directions (must be odd number).; Fetch computed as an average of multiple minor directions around each direction.; Options: 1-360; Default: 5
minor_step=integer [required]: Angular step size between minor directions.; Fetch computed as an average of multiple minor directions around each direction.; Options: 1-180; Default: 3
output_file=name: If not given write to standard output
format=string: Output format; Options: csv, json; Default: csv; csv: CSV (Comma Separated Values); json: JSON (JavaScript Object Notation)

DESCRIPTION
NOTES
EXAMPLE
SEE ALSO
AUTHORS

DESCRIPTION

The purpose of r.windfetch is to compute wind fetch, which is the length of water over which winds blow without obstruction. Fetch is an important feature in wave modeling for waves created by wind.

Input is a binary raster map input where land is 1 and 0 is water. To compute fetch for certain point(s), user provides either the coordinates with the coordinates parameter or a points vector map with points parameter. Output is formatted with format parameter either as JSON or CSV and can be printed to a file (output_file) or to standard output.

NOTES

Wind fetch is computed for specific directions, determined by parameters direction and step. Direction angle is in degrees counterclockwise from the East. For example, for direction=45 and step=90, r.windfetch computes fetch for directions 45, 135, 225, and 315 (NE, NW, SW, SE). By default wind fetch for each direction is averaged from multiple directions around it. The number of minor directions from which the main direction is computed is specified with parameter minor_directions. The step between the minor directions is given in minor_step and is in degrees.

EXAMPLE

Compute wind fetch on a lake edge with default parameters:

r.mapcalc "land = if (isnull(lakes), 1, 0)"
r.windfetch input=land format=csv coordinates=635659,223234

Figure: Wind fetch for a selected point, visualized in a polar plot.

AUTHORS

Anna Petrasova, NCSU GeoForAll Lab. This addon was developed with funding from NSF Award #2322073, granted to Natrx, Inc.

SOURCE CODE

Available at: r.windfetch source code (history)

Latest change: Monday Aug 05 10:08:07 2024 in commit: c254d5268f792acd1e804143672dea374591c439