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 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

Value

SpatRaster

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))