Hi Thiago,
calc is not aware of neighbouring pixels in the x,y dimensions, so
functions like focal cannot work.
I found the function below in an old repos of mine. It still seems to
work fine :)
#' Focal for RasterBrick or RasterStack
#'
#' @param x RasterBrick/Stack or character pointing to multilayer raster
object written on disk
#' @param w See \code{\link{focal}}
#' @param ... Arguments to be passed to \code{\link{focal}}
#'
#' @import raster
#' @export
#'
multiFocal <- function(x, w=matrix(1, nr=3, nc=3), ...) {
if(is.character(x)) {
x <- brick(x)
}
# The function to be applied to each individual layer
fun <- function(ind, x, w, ...){
focal(x[[ind]], w=w, ...)
}
n <- seq(nlayers(x))
list <- lapply(X=n, FUN=fun, x=x, w=w, ...)
out <- stack(list)
return(out)
}
On 05/21/2016 10:02 PM, Thiago V. dos Santos via R-sig-Geo wrote:
I have a multi-layer raster, in this case a rasterbrick, on which I would like
to apply a focal function on each layer, and get another rasterbrick as a
result.
I am trying to use calc, but apparently I am not assembling my function in the
proper way:
require(raster)
r <- raster(ncol=50, nrow=50)
r[]=1:ncell(r)
b <- brick(r,r,r,r,r,r)
b <- b * 1:6
multiFocal(b, w=matrix(1, 5, 5), mean)
Cheers,
Loïc
myfocalfun <- function(x){
b.f <- focal(x, w=matrix(1, 5, 5), mean)
return(b.f)
}
b1 <- calc(b, myfocalfun)
Error in .calcTest(x[1:5], fun, na.rm, forcefun, forceapply) :
cannot use this function
What am I missing here?
Greetings,
-- Thiago V. dos Santos
PhD student
Land and Atmospheric Science
University of Minnesota
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