terra (version 1.0-10)

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, na.only=FALSE, 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 weights matrix . See Details. If w is a matrix, na.rm=FALSE and fun=sum, and cannot be changed

na.rm

logical. Should missing values be removed?

na.only

logical. Should only missing values in x be changed?

fillvalue

numeric. The value of the cells in the virtual rows and columns outside of the raster

fun

function that takes multiple numbers, and returns a single number. For example mean, modal, min or max. It should also accept a na.rm argument, either as actual argument or through use of ...

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 use a matrix and 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)
# }