center
logical or numeric. If TRUE, centering is done by subtracting the layer means (omitting NAs), and if FALSE, no centering is done. If center is a numeric vector with length equal to the nlayers(x)
scale
logical or numeric. If TRUE, scaling is done by dividing the (centered) layers of x by their standard deviations if center is TRUE, and the root mean square otherwise. If scale is FALSE, no