man/examples/ex_ruggedness_wetness.r

In fasterRaster: Faster Raster and Spatial Vector Processing Using 'GRASS GIS'

if (grassStarted()) {

# Setup
library(terra)

# Elevation raster
madElev <- fastData("madElev")

# Convert to GRaster:
elev <- fast(madElev)

# Terrain ruggedness index:
tri <- ruggedness(elev)
plot(c(elev, tri))

# Topographic wetness index:
twi <- wetness(elev)
plot(c(elev, twi))

}