Sieve filter

Apply a sieve filter. That is, remove "noise", by changing small clumps of cells with a value that is different from the surrounding cells, to the value of the largest neighboring clump.

Note that the input raster data is rounded to integers.

Usage

# S4 method for class 'SpatRaster'
sieve(x, threshold, directions=8, filename="", ...)

Arguments

x

SpatRaster, single layer with elevation values. Values should have the same unit as the map units

threshold

positive integer. Only clumps smaller than this threshold will be removed

directions

numeric to indicate which cells are connected. Either 4 to only consider the horizontal and vertical neighbors ("rook"), or 8 to consider the vertical, horizontal and diagonal neighbors

filename

character. Output filename

...

Options for writing files as in writeRaster

See also

focal

Examples

r <- rast(nrows=18, ncols=18, xmin=0, vals=0, crs="local")
r[2, 5] <- 1
r[5:8, 2:3] <- 2
r[7:12, 10:15] <- 3
r[15:16, 15:18] <- 4
freq(r, bylayer=FALSE)
#>   value count
#> 1     0   271
#> 2     1     1
#> 3     2     8
#> 4     3    36
#> 5     4     8

x <- sieve(r, 8)
y <- sieve(r, 9)