**-s**- Use square moving window instead of circular moving window
**--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

**elevation**=*name***[required]**- Name of elevation raster map
**mrvbf**=*name***[required]**- Name of output MRVBF raster map
**mrrtf**=*name*- Name of output MRRTF raster map
**t_slope**=*string*- Initial Threshold for Slope
- Default:
*16* **t_pctl_v**=*string*- Threshold (t) for transformation of Elevation Percentile (Lowness)
- Default:
*0.4* **t_pctl_r**=*string*- Threshold (t) for transformation of Elevation Percentile (Upness)
- Default:
*0.3* **t_vf**=*string*- Threshold (t) for transformation of Valley Bottom Flatness
- Default:
*0.3* **t_rf**=*string*- Threshold (t) for transformation of Ridge Top Flatness
- Default:
*0.35* **p_slope**=*string*- Shape Parameter (p) for Slope
- Default:
*4* **p_pctl**=*string*- Shape Parameter (p) for Elevation Percentile
- Default:
*3* **min_cells**=*string*- Minimum number of cells in generalized DEM
- Default:
*2*

*t_slope*represents the initial threshold (t) for slope angle (in percentage). This specifies the slope angle that corresponds to a (logit) rescaled flatness value of 0.5. This means that slope angles lower than t_slope will be considered as flat areas, and slope angles higher than t_slope will be represented as non-flat areas. t_slope should be set based on the resolution of the input elevation dataset, and the algorithm was designed using with a 25 m DEM having a t_slope value of 16. Otherwise the t_slope value should by halved for every resolution step (a step consisting of a 3 x coarsening of resolution) above a 25 m resolution. For example, a 75 m DEM (3 x 25 m, 1 step) should have a t_slope value of 8, and a 250 m DEM (~2 resolution steps) should have a t_slope value of 4.*p_slope*represents the shape parameter (p) for the sigmoid transformation. It defines the slope of the sigmoid function, i.e. how quickly changes in slope angle scale to being flat vs. non-flat areas. High p_slope values will cause a slow, smooth transition from flat areas to steep areas. Low p_slope values will result in much more rapid transitions that highlight more local vs. regional relief.*t_pctl_v*represents the threshold for transformation of elevation percentile to evaluate lowness. This represents the threshold value for elevation percentile by which values less than this value will represent low areas. Elevation percentile represents the ratio of pixels of lower elevation relative to the total number of pixels in a moving-window neighborhood. Similarly*t_pctl_r*is the equivalent 'upness' threshold for the MRRTF index.*p_pctl*represents the shape parameter (p) for the transformation of the elevation percentile. It defines the slope of the sigmoid function and governs how quickly transitions occur from low areas to upland areas.*t_vf*and*t_rf*represent the thresholds for identifying valley bottoms (or ridge tops). Larger values indicate increasing valley bottom characteristics, with values < 0.5 considered not to be in valley bottoms.

The calculation of elevation percentile by default is performed using a circular window. With the **-s** flag a square moving window is used in calculations.

In practice, the user does not usually need to alter the threshold-related parameters other than t_slope. However, changing the shape parameters can be useful for to emphasize more local vs. more regional variations in relief. The degree of generalization can also be adjusted by the *min_cells* argument. The default value of 1 is equivalent to generalizing the input **elevation** raster to 100 percent of its original cell size. To reduce processing time, or focus the results on more local-relief, try increasing the number of min_cells.

Here we are going to use the GRASS GIS sample North Carolina data set as a basis to calculate the MRVBF index.

# align region to DEM g.region -a raster=el_D782_6m # runr.valley.bottomr.valley.bottom elevation=el_D782_6m mrvbf=mrvbf_el_D782_6m t_slope=40 p_slope=3 p_pctl=2 # set colors r.colors map=mrvbf_el_D782_6m color=bcyr -n # display over a shaded relief map r.relief input=el_D782_6m output=hs_D782_6m altitude=45 azimuth=315 zscale=4 scale=1 r.shade shade=hs_D782_6m color=mrvbf_el_D782_6m output=mrvbf_shade d.rast map=mrvbf_shade

Available at: r.valley.bottom source code (history)

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