Mask values in a raster

The output of mask() is a GRaster that has the same as values as the input raster. However, if the mask argument is a GRaster, the output will have NA values in the same cells that the mask raster has NA cells. If the mask argument is a GVector, then the output raster will have NA values in cells the GVector does not cover.

Usage

# S4 method for class 'GRaster,GRaster'
mask(x, mask, inverse = FALSE, maskvalues = NA, updatevalue = NA)

# S4 method for class 'GRaster,GVector'
mask(x, mask, inverse = FALSE, updatevalue = NA)

Arguments

x

A GRaster.

mask

A GRaster or GVector.

inverse

Logical: If TRUE, the effect of the mask is inverted. That is, a copy of the input raster is made, but cells that overlap with an NA in the mask raster or are not covered by the mask vector retain their values. Cells that overlap with an NA in the mask raster or overlap with the mask vector are forced to NA.

maskvalues

Numeric vector, including NA (only for when mask is a GRaster): The value(s) in the mask raster cells that serve as the mask. The default is NA, in which case cells in the input raster that overlap with NA cells in the mask are forced to NA.

updatevalue

Numeric, including NA (default): The values assigned to masked cells.

Value

A GRaster.

See also

terra::mask(), GRASS module r.mask

Examples

if (grassStarted()) {

# Setup
library(sf)
library(terra)

# Example data
madElev <- fastData("madElev") # raster
madForest <- fastData("madForest2000") # raster
madCoast <- fastData("madCoast4") # vector

# Convert to GRasters and GVectors
elev <- fast(madElev)
forest <- fast(madForest)
coast <- fast(madCoast)

ant <- coast[coast$NAME_4 == "Antanambe"]

# Mask by a raster or  vector:
maskByRast <- mask(elev, forest)
plot(c(forest, maskByRast))

maskByVect <- mask(elev, ant)
plot(maskByVect)
plot(ant, add = TRUE)

# Mask by a raster or vector, but invert mask:
maskByRastInvert <- mask(elev, forest, inverse = TRUE)
plot(c(forest, maskByRastInvert))

maskByVectInvert <- mask(elev, ant, inverse = TRUE)
plot(maskByVectInvert)
plot(ant, add = TRUE)

# Mask by a raster, but use custom values for the mask:
maskByRastCustomMask <- mask(elev, elev, maskvalues = 1:20)
plot(c(elev <= 20, maskByRastCustomMask))

# Mask by a raster or vector, but force masked values to a custom value:
byRastCustomUpdate <- mask(elev, forest, updatevalue = 7)
plot(byRastCustomUpdate)

byVectCustomUpdate <- mask(elev, ant, updatevalue = 7)
plot(byVectCustomUpdate)

# Mask by a raster, inverse, custom values, and custom update:
byRastAll <-
   mask(elev, elev, inverse = TRUE, maskvalues = 1:20, updatevalue = 7)

plot(c(elev, byRastAll))

}