## 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 g.gui.rlisetup, then the output will be a raster map, otherwise an ASCII file will be generated in the folder `C:\Users\userxy\AppData\Roaming\GRASS8\r.li\output\` (MS-Windows) or `$HOME/.grass8/r.li/output/` (GNU/Linux).

A sample area of only NULL values is considered to have zero patches, that is, the result is always ≥ 0.

## EXAMPLES

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

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

Example for Spearfish forest areas:

    g.region raster=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 g.gui.rlisetup):
    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 raster=landclass96 -p
    r.mapcalc "forests = if(landclass96 == 5, 1, null() )"
    r.li.patchdensity input=forests conf=movwindow7 out=forests_patchdensity_mov7

    # verify
    r.univar forests_patchdensity_mov7
    r.to.vect input=forests output=forests type=area
    d.mon wx0
    d.rast forests_patchdensity_mov7
    d.vect forests type=boundary

## SEE ALSO

r.li - package overview, g.gui.rlisetup

## 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

Michael Shapiro - CERL (patch identification)
Markus Metz (statistics)