kde2d.G {GRASS}R Documentation

Two-Dimensional Kernel Density Estimation on a GRASS Grid

Description

A version of kde2d() in the MASS package of the VR collection using the metadata of the underlying GRASS LOCATION. kde2d() is for "two-dimensional kernel density estimation with an axis-aligned bivariate normal kernel, evaluated on a square grid." An optional feature is the introduction of a weighted moving average through the Z argument.

Usage

kde2d.G(G, x, y, h, reverse=NULL, Z=NULL)

Arguments

G GRASS metadata from gmeta()
x x coordinate of data
y y coordinate of data
h vector of bandwidths for x and y directions. Defaults to normal reference bandwidth.
reverse see help(reverse)
Z vector of attribute values

Value

A vector of G$Ncells values is returned, with the results of density/weighted moving average calculations ordered as a GRASS raster file. Density values are points per unit area, while moving average values are in the units of the Z variable.

Note

The functions in this package are intended to work with the GRASS geographical information system. The examples for wrapper functions will will work whether or not R is running in GRASS, and whether or not the current location is that of the data set used for the examples. Examples of interface functions will however (from version 0.2-2) only work outside GRASS, to avoid possible overwriting of GRASS database locations and/or files.

Author(s)

Original kde2d(), bandwidth.nrd(): Brian D. Ripley and Bill Venables as detailed in the MASS package documentation; adapted by Roger S. Bivand, e-mail: Roger.Bivand@nhh.no.

References

http://grass.itc.it/statsgrass/index.html, Bivand, R. S., (2000) Using the R statistical data analysis language on GRASS 5.0 GIS data base files. Computers and Geosciences, 26, pp. 1043-1052.

See Also

kde2d

Examples

data(utm.maas)
G <- maas.metadata
inregion <- (utm.maas$east >= G$w & utm.maas$east <= G$e) &
  (utm.maas$north >= G$s & utm.maas$north <= G$n)
if(all(!inregion)) stop("None of the site locations are inside the current GRASS region")
if(any(!inregion)) warning("Some site locations are outside the current GRASS region")
plot(G, kde2d.G(G=G, utm.maas$east, utm.maas$north, h=c(300,300))*maasmask)
points(utm.maas$east, utm.maas$north)
rug(utm.maas$east, side=1, ticksize=0.02)
rug(utm.maas$north, side=2, ticksize=0.02)
title(main="Kernel estimates of density of soil sample placing",
  xlab="(Bailey & Gatrell, pp. 84-88")
plot(G, kde2d.G(G=G, utm.maas$east, utm.maas$north, h=c(300,300), Z=utm.maas$Zn)*maasmask)
points(utm.maas$east, utm.maas$north)
rug(utm.maas$east, side=1, ticksize=0.02)
rug(utm.maas$north, side=2, ticksize=0.02)
title(main="Kernel density weighted average, Zn ppm",
  xlab="(Bailey & Gatrell, pp. 159-161")

[Package GRASS version 0.3-7 Index]