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Note: This document is for an older version of GRASS GIS that will be discontinued soon. You should upgrade, and read the current manual page.


r.droka - Calculates run-out distance of a falling rock mass


rock mass, rockfall


r.droka --help
r.droka dem=string start=string ang=float red=float m=float num=integer prefix=name [n=integer] [--overwrite] [--help] [--verbose] [--quiet] [--ui]


Allow output files to overwrite existing files
Print usage summary
Verbose module output
Quiet module output
Force launching GUI dialog


dem=string [required]
Digital Elevation Model
start=string [required]
Name of starting points map
ang=float [required]
Shadow angle
red=float [required]
Reduction value
Options: 0-1
Default: 0.9
m=float [required]
Value of rock mass (kg)
num=integer [required]
Number of boulders (>=1)
prefix=name [required]
Prefix for output raster maps
Buffer distance (meters)

Table of contents


The intersection between the topographic profile and the line starting from the point of detachment with a certain angle to the horizontal line defines the point of maximum propagation (Evans and Hungr, 1993; Jaboyedoff and Labiouse, 2003). The angle of inclination and the line of propagation are defined as zenith angle and shadow zone. This script defines rockfall zones from a digital elevation model (DEM) and vector layer containing starting point or points.

Energy line used for the cone method from the top or the bottom of a cliff (shadow angle), according to various authors (Image from Jaboyedoff and Labiouse, 2003)


Digital Elevation Model = name

Starting points = name

Shadow angle = integer

Reduction value = double

Number of boulders = integer

Rock mass = double

Output prefix = string

Buffer distance = integer


r.droka generates 5 raster maps and a vector map. The names of all output maps start with the prefix defined by the parameter prefix followed by the name of map


FILIPELLO A., GIULIANI A., MANDRONE G. (2010) - Rock Slopes Failure Susceptibility Analysis: From Remote Sensing Measurements to Geographic Information System Raster Modules. American Journal of Environmental Sciences 6 (6): 489-494, 2010 ISSN 1553-345X 2010 Science Publications.

JABOYEDOFF M., LABIOUSE V. (2003) - Preliminary assessment of rockfall hazard based on GIS Data. Proceeding of the 10th ISRM Congress, South African Inst. Min. Met., Johannesburg, pp: 575-578

EVANS, S.G., HUNGR O. (1993). The assessment of rock fall hazard at the base of the talus slope. Can. Geotech. J., 30: 620-636. DOI: 10.1139/t93-054



Andrea Filipello, University of Turin, Italy

Daniele Strigaro, University of Milan, Italy


Available at: r.droka source code (history)

Latest change: Monday Jan 30 19:52:26 2023 in commit: cac8d9d848299297977d1315b7e90cc3f7698730

Note: This document is for an older version of GRASS GIS that will be discontinued soon. You should upgrade, and read the current manual page.

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