GRASS GIS manual: r.li.patchdensity

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NAME

r.li.patchdensity - Calculates patch density index on a raster map, using a 4 neighbour algorithm

KEYWORDS

raster, landscape structure analysis, patch index

SYNOPSIS

r.li.patchdensity
r.li.patchdensity help
r.li.patchdensity map=name conf=name output=name [--overwrite] [--verbose] [--quiet]

Flags:

--overwrite: Allow output files to overwrite existing files
--verbose: Verbose module output
--quiet: Quiet module output

Parameters:

map=name: Name of input raster map
conf=name: Configuration file
output=name: Name for output raster map

DESCRIPTION

r.li.patchdensity calculates the "patch density index", the number of patches per square kilometer, as:

PD = Npatch / A

with:

A:sampling area size
Npatch: number of patches

This index is calculated using a 4 neighbour algorithm, diagonal cells are ignored when tracing a patch.

NOTES

Do not use absolute path names for the config and output file/map parameters. If the "moving window" method was selected in r.li.setup, then the output will be a raster map, otherwise an ASCII file will be generated in the folder C:\Users\userxy\.r.li\output\ (MS-Windows) or $HOME/.r.li/output/ (GNU/Linux).

A map of NULL values is considered to have zero patches.
If raster area is 0, r.li.patchdensity returns -1. This is only possible if the raster is masked.
If you want to change these -1 values to NULL, run subsequently on the resulting map:

r.null setnull=-1 map=my_out

after index calculation.

EXAMPLES

To calculate patch density index on map my_map, using my_conf configuration file (previously defined with r.li.setup) and saving results in my_out, run:

r.li.patchdensity map=my_map conf=my_conf output=my_out

Example for Spearfish forest areas:

g.region rast=landcover.30m -p
# extract forested areas:
r.category landcover.30m
r.mapcalc "forests = if(landcover.30m >= 41 && landcover.30m <= 43, 1, null())"

# patch density (7x7 moving window defined in r.li.setup):
r.li.patchdensity forests conf=movwindow7 out=forests_p_dens7
r.univar forests_p_dens7
d.rast.leg forests_p_dens7

r.to.vect forests out=forests feature=area
d.vect forests type=boundary

Forest map (North Carolina sample dataset) example:

g.region rast=landclass96 -p
r.mapcalc "forests = if(landclass96 == 5, 1, null() )"
r.li.patchdensity map=forests conf=movwindow7 out=forests_patchdensity_mov7

# verify
r.univar forests_patchdensity_mov7
r.to.vect input=forests output=forests feature=area
d.mon x0
d.rast forests_patchdensity_mov7
d.vect forests type=boundary

REFERENCES

McGarigal, K., and B. J. Marks. 1995. FRAGSTATS: spatial pattern analysis program for quantifying landscape structure. USDA For. Serv. Gen. Tech. Rep. PNW-351. (PDF)

AUTHORS

Claudio Porta and Lucio Davide Spano, students of Computer Science University of Pisa (Italy).
Commission from Faunalia Pontedera (PI) (www.faunalia.it)
Markus Metz (statistics)

Last changed: $Date: 2014-10-19 14:32:22 -0700 (Sun, 19 Oct 2014) $

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