ST_TRI — Returns a raster with the calculated Terrain Ruggedness Index.
raster ST_TRI(raster  rast, integer  nband, raster  customextent, text  pixeltype="32BF" , boolean   interpolate_nodata=FALSE  );
Terrain Ruggedness Index is calculated by comparing a central pixel with its neighbors, taking the absolute values of the differences, and averaging the result.
                 
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                 This function only supports a focalmean radius of one.  | 
            
Availability: 2.1.0
-- needs examples