spatialEco (version 2.0-2)

tri: Terrain Ruggedness Index

Description

Implementation of the Riley et al (1999) Terrain Ruggedness Index

Usage

tri(r, s = 3, exact = TRUE, ...)

Value

A terra SpatRaster class object of the TRI

Arguments

r

A terra SpatRaster class object

s

Scale of window. Must be odd number, can represent 2 dimensions (eg., s=c(3,5) would represent a 3 x 5 window)

exact

Calculate (TRUE/FALSE) the exact TRI or an algebraic approximation.

...

Additional arguments passed to terra::focal or terra::app

Author

Jeffrey S. Evans

Details

The algebraic approximation is considerably faster. However, because inclusion of the center cell, the larger the scale the larger the divergence of the minimum value. Resuls are driven by local variations so, fixed thresholds are not very reliable. However there are some reccomended breaks (eg., Riley et al., 1999).

Riley et al., (1999) ranges for classifying Topographic Ruggedness Index:

• 0-80 - level terrain surface.

• 81-116 - nearly level surface.

• 117-161 - slightly rugged surface.

• 162-239 - intermediately rugged surface.

• 240-497 - moderately rugged surface.

• 498-958 - highly rugged surface.

• gt 959 - extremely rugged surface.

References

Riley, S.J., S.D. DeGloria and R. Elliot (1999) A terrain ruggedness index that quantifies topographic heterogeneity, Intermountain Journal of Sciences 5(1-4):23-27.

Examples

# \donttest{
library(terra)
elev <- rast(system.file("extdata/elev.tif", package="spatialEco"))
  ( tri.ext <- tri(elev) )
  ( tri.app <- tri(elev, exact = FALSE) )
  plot(c(tri.ext, tri.app))
# }