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r.tri - Computes the Terrain Ruggedness Index.



r.tri --help
r.tri [-c] input=name output=name size=integer [--overwrite] [--help] [--verbose] [--quiet] [--ui]


Use circular neighborhood
Allow output files to overwrite existing files
Print usage summary
Verbose module output
Quiet module output
Force launching GUI dialog


input=name [required]
Input elevation raster
output=name [required]
Output Terrain Ruggedness Index (TRI)
size=integer [required]
Size of neighbourhood in cells
Default: 3

Table of contents


r.tri calculates the Terrain Ruggedness Index (TRI) of Riley et al. (1999). The index represents the mean change in elevation between a grid cell and its neighbours, over a user-specified moving window size. The original calculation in Riley et al. (1999) used only a 3x3 neighbourhood and represented the sum of the absolute deviations between the center pixel and its immediate 8 neighbours. In r.tri, this calculation is modified so that the calculation can be extended over any scale by taking the mean of the absolute deviations.


r.tri produces fairly similar results to the average deviation of elevation values, apart from the center pixel is used in place of the mean. In practice, this produces a slightly less smoothed result that can potentially better highlight finer-scale terrain features.

Similar to many other GRASS GIS algorithms, cell padding is not performed automatically which will leave null values at the boundaries of the output raster relative to the size of the input raster. To minimize this effect the DEM needs to be buffered/grown prior to using r.tri.

To reduce computational times for large raster datasets, setting n_jobs > 1 will use a parallelized and tiled calculations that is spread across multiple processing cores. This option requires the GRASS addon r.mapcalc.tiled to be installed.


d.rast map=elev_lid792_1m@PERMANENT
g.region raster=elev_lid792_1m@PERMANENT -a
r.tri input=elev_lid792_1m@PERMANENT size=9 output=tri
Terrain Ruggedness Index


Riley, S. J., S. D. DeGloria and R. Elliot (1999). A terrain ruggedness index that quantifies topographic heterogeneity, Intermountain Journal of Sciences, vol. 5, No. 1-4, 1999.


r.mapcalc, r.mapcalc.tiled


Steven Pawley


Available at: r.tri source code (history)

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