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List: r-sig-geo
Subject: Re: [R-sig-Geo] Run focal function on a multi-layer raster
From: "Thiago V. dos Santos via R-sig-Geo" <r-sig-geo () r-project ! org>
Date: 2016-05-21 22:24:26
Message-ID: 1714185786.313852.1463869466417.JavaMail.yahoo () mail ! yahoo ! com
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Hi Loïc,
Thanks for the hint - it worked like a charm!
Greetings,
-- Thiago V. dos Santos
PhD student
Land and Atmospheric Science
University of Minnesota
On Saturday, May 21, 2016 3:54 PM, Loïc Dutrieux <loic.dutrieux@wur.nl> wrote:
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
>
> _______________________________________________
> R-sig-Geo mailing list
> R-sig-Geo@r-project.org
> https://stat.ethz.ch/mailman/listinfo/r-sig-geo
>
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