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r.tri - 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 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, which in some cases can better highlight smaller-scale terrain features. Like in many GRASS GIS algorithms, cell padding is not performed automatically and there will be an edge effect. The resulting TRI will not be calculated at the image edges so there will be missing pixels along the margins relative to the size of the input raster. To minimize this effect the flag -p can be set to grow the DEM by the chosen radius prior to the TRI calculation.


r.tri input=srtm size=1 output=tri


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.


Steven Pawley


Available at: r.tri source code (history)

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