**-c**- Use circular neighborhood
**--overwrite**- Allow output files to overwrite existing files
**--help**- Print usage summary
**--verbose**- Verbose module output
**--quiet**- Quiet module output
**--ui**- 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 (> 2 and <= 51)
- Default:
*3* **exponent**=*float*- Distance weighting exponent (>= 0 and <= 4.0)
- Default:
*0.0* **processes**=*integer*- Number of processing cores for tiled calculation
- Number of processing cores for tiled calculation (negative numbers are all cpus -1, -2 etc.)
- Default:
*1*

*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 highlight finer-scale terrain features. However, because the
terrain ruggedness index does not consider the distance of each cell from
the centre cell in it's calculation, the TRI results can become noisy with
large window sizes. To avoid this, weighting each cell by the inverse of
its distance can be used by setting the *exponent* parameter to > 0.

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.

Currently, *r.tri* is implemented using a *r.mapcalc* focal
function. This becomes slow for large window sizes. To reduce computational
times for large raster datasets, setting *processes* parameter to
> 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

Available at: r.tri source code (history)

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