terra (version 0.5-8)

focal: Focal values

Description

Calculate focal ("moving window") values for the neighborhood of focal cells using a matrix of weights, perhaps in combination with a function.

Usage

# S4 method for SpatRaster
focal(x, w=3, na.rm=TRUE, fillvalue=NA, fun="sum", 
            filename="", overwrite=FALSE, wopt=list(), ...)

Arguments

x

SpatRaster

w

window. The window can be defined as one (for a square) or two numbers (row, col); or with an odd-sized matrix with weights. See Details. If the window is defined as a matrix, na.rm=FALSE and fun=sum, and cannot be changed

na.rm

logical. Should missing values be removed?

fillvalue

numeric. The value of the cells of the padded rows and columns

fun

function. The function fun should take multiple numbers, and return a single number. For example mean, modal, min or max. It should also accept a na.rm argument

filename

character. Output filename. Optional

overwrite

logical. If TRUE, filename is overwritten

wopt

list. Options for writing files as in writeRaster

...

additional arguments. None implemented

Value

SpatRaster

Details

focal

The window used must have odd dimensions. If you need even sides, you can make a matrix add a column or row with weights of zero.

Example weight matrices

Laplacian filter: filter=matrix(c(0,1,0,1,-4,1,0,1,0), nrow=3)

Sobel filter: filter=matrix(c(1,2,1,0,0,0,-1,-2,-1) / 4, nrow=3)

Examples

# NOT RUN {
r <- rast(ncols=10, nrows=10, ext(0, 10, 0, 10))
values(r) <- 1:ncell(r)

f <- focal(r, w=3, fun=function(x, ...)quantile(x, .25, ...), na.rm=TRUE) 

f <- focal(r, w=3, fun="mean") 

# the following two statements are equivalent:
a <- focal(r, w=matrix(1/9, nc=3, nr=3))
b <- focal(r, w=3, fun=mean, na.rm=FALSE)

# but this is different
d <- focal(r, w=3, fun=mean, na.rm=TRUE)
# }