focalFilter: Focal filter

Description

Calculate values for the neighborhood of focal cells using a matrix of weights

Usage

focalFilter(x, filter, fun=sum, filename="", na.rm=FALSE, pad=TRUE, padValue=NA, ...)

Arguments

A RasterLayer object

filter

a matrix of weights. See Details

fun

a function to apply to the product of the matrix of weights and the values

filename

Output filename for a new raster

na.rm

Boolean. If TRUE, NA values are ignored. Except for some special cases, this is generally not a good idea in this function because it will unbalance the effect of the filter!

pad

Boolean. If TRUE, additional 'virtual' rows and columns are padded to x such that there are no edge effects. This can be useful when a function needs to have access to the central cell of the filter.

padValue

Boolean. The value of the cells of the padded rows and columns. This value is ignored if x is unprojected (latiude/longitude) and spans all longitudes (-180 to 180 degrees)

...

additional arguments. See Details.

Value

A new RasterLayer object (in the R environment), and in some cases the side effect of a new file on disk.

Details

focalFilter uses a matrix of weights for the neigbhorhood of the focal cells, together with a function (normally sum). For example, filter=matrix(1/9, nrow=3, ncol=3) would be equivalent to mean with ngb=3 in the focal function. Gaussian filter: filter=matrix(c(1,2,3,2,1,2,3,4,3,2,3,4,5,4,3,2,3,4,3,2,1,2,3,2,1), nrow=5)/65 Laplacian filter: filter=matrix(c(0,1,0,1,-4,1,0,1,0), nrow=3) Sobel filter: filter=matrix(c(1,2,1,0,0,0,-1,-2,-1) / 4, nrow=3) Another example: filter=matrix(c(0,0,0,0,1,1,0,1,1), nrow=3) and fun=max returns the max value for the lower-rigth corner of a 3x3 matrix around a focal cell The filter must have uneven sides (e.g., 3x3 or 5x5), but if you need uneven sides, you can add a column or row with weights of zero. The following additional arguments can be passed, to replace default values for this function rll{ overwrite Logical. If TRUE, "filename" will be overwritten if it exists format Character. Output file type. See writeRaster datatype Character. Output data type. See dataType progress Character. "text", "window", or "" (the default, no progress bar) }

Examples

Run this code

r <- raster(ncols=36, nrows=18)
r[] <- runif(ncell(r)) 
gf=matrix(c(1,2,3,2,1,2,3,4,3,2,3,4,5,4,3,2,3,4,3,2,1,2,3,2,1), nrow=5)/65
rff <- focalFilter(r, filter = gf)