r.vector.ruggedness represents a measurement of terrain ruggedness based on the methodology conceived by Sappington et al. (2007). The measure is calculated by decomposing slope and aspect into 3-dimensional vectors, and calculating the resultant vector magnitude within a user-specified moving window size using r.neighbors. The user can specify neighborhood size to measure ruggedness across larger scales. Neighborhood operations are performed using a rectangular window shape.
The r.vector.ruggedness tool provides an efficient approach of calculating the Vector Ruggedness Measure over multiple window sizes. The size argument accepts multiple answers (as a comma separated list), which will cause the tool to reuse the same slope, aspect and vector calculations, and apply them to the neighborhood operations that calculate the vector magnitudes. By default, both the calculation of the vectors and the vector magnitudes, including over different window sizes is performed in parallel using all available cores. To restrict parallel processing, the nprocs argument can be changed to use a smaller number of processing cores. When multiple sizes are used, the output raster name is appended with the window size. Optionally, pre-calculated slope and aspect maps (in degrees) can be used in the slope and aspect arguments to save computational time if the maps are already available.
This script was adapted from the original Sappington et al. (2007) script.
The examples are to be executed using the GRASS GIS sample North Carolina data set. To calculate the Vector Ruggedness Measure using a single neighborhood size:
r.vector.ruggedness elevation=elevation size=3 output=vrm
For efficient calculations of the Vector Ruggedness Measure over multiple neighborhood sizes, the slope, aspect and their x, y, z vectors will be reused during the calculation. The output name will be appended with the neighborhood size in order to identify the output maps:
r.vector.ruggedness elevation=elevation size=3,5,7,9,11 output=vrm
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