Focal weights matrix — focalWeight • raster

Calculate focal ("moving window") weight matrix for use in the focal function. The sum of the values adds up to one.

focalWeight(x, d, type=c('circle', 'Gauss', 'rectangle'), fillNA=FALSE)

Arguments

x: Raster* object
d: numeric. If type=circle, the radius of the circle (in units of the CRS). If type=rectangle the dimension of the rectangle (one or two numbers). If type=Gauss the size of sigma, and optionally another number to determine the size of the matrix returned (default is 3 times sigma)
type: character indicating the type of filter to be returned
fillNA: logical. If TRUE, zeros are set to NA such that they are ignored in the computations. Only applies to type="circle"

Value

matrix that can be used in focal

Examples

r <- raster(ncols=180, nrows=180, xmn=0, crs="+proj=utm +zone=1")
# Gaussian filter for square cells
gf <- focalWeight(r, .5, "Gauss")
focalWeight(r, 2, "circle", fillNA=TRUE)
#>            [,1]       [,2]       [,3]       [,4]       [,5]
#> [1,]         NA         NA 0.07692308         NA         NA
#> [2,]         NA 0.07692308 0.07692308 0.07692308         NA
#> [3,] 0.07692308 0.07692308 0.07692308 0.07692308 0.07692308
#> [4,]         NA 0.07692308 0.07692308 0.07692308         NA
#> [5,]         NA         NA 0.07692308         NA         NA