focalPairs function

Focal function across two layers

Calculate values such as a correlation coefficient for focal regions in two neighboring layers. A function is applied to the first and second layer, then to the second and third layer, etc.

## S4 method for signature 'SpatRaster'
focalPairs(x, w=3, fun, ..., fillvalue=NA, 
                filename="", overwrite=FALSE, wopt=list())

Arguments

• x: SpatRaster with at least two layers
• w: numeric or matrix to define the focal window. The window an be defined as one (for a square) or two numbers (row, col); or with an odd-sized weights matrix. See the Details section in focal. Note that if a matrix with numbers other than zero or one are used, the values are used as weights. For this to work, fun must have an argument weights
• fun: a function with at least two arguments (one for each layer). There is a built-in function "pearson" (for both the weighted and the unweighted Pearson correlation coefficient. This function has an additional argument na.rm=FALSE
• ...: additional arguments for fun
• fillvalue: numeric. The value of the cells in the virtual rows and columns outside of the raster
• filename: character. Output filename
• overwrite: logical. If TRUE, filename is overwritten
• wopt: additional arguments for writing files as in writeRaster

Returns

SpatRaster

See Also

layerCor, focalReg, focal, focal3D

Examples

r <- rast(system.file("ex/logo.tif", package="terra"))
set.seed(0)
r[[1]] <- flip(r[[1]], "horizontal")
r[[2]] <- flip(r[[2]], "vertical") + init(rast(r,1), runif)
r[[3]] <- init(rast(r,1), runif)

x <- focalPairs(r, w=5, "pearson", na.rm=TRUE)
plot(x)

# suppress warning "the standard deviation is zero"
suppressWarnings(x <- focalPairs(r, w=5, "pearson", use="complete.obs"))

z <- focalPairs(r, w=9, function(x, y) mean(x) + mean(y))