It should be possible to use it for ratings on all layers.
Examples
if (FALSE) { # \dontrun{
x <- randomGrid()
x[1, 1] <- 2
x[1, ] <- 4
x[, 2] <- 3
# settings values outside defined rating scale
# range throws an error
x[1, 1] <- 999
# removing scale range allows arbitary values to be set
x <- setScale(x, min = NA, max = NA)
x[1, 1] <- 999
} # }