r.skyview - GRASS manual

NAME

r.skyview - Computes skyview factor visualization technique.

KEYWORDS

SYNOPSIS

r.skyview

r.skyview --help

r.skyview [-on] input=name output=name ndir=integer [maxdistance=float] [color_source=string] [color_input=name] [color_table=string] [colorized_output=name] [basename=string] [nprocs=integer] [memory=memory in MB] [--overwrite] [--help] [--verbose] [--quiet] [--ui]

Flags:

-o: Compute openness instead of skyview factor; Openness considers zenith angles > 90 degrees
-n: Invert color table for colorization raster; Ignored for input and color_input
--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

Parameters:

input=name [required]: Name of input raster map
output=name [required]: Name for output raster map
ndir=integer [required]: Number of directions (8 to 32 recommended); Options: 2-360; Default: 16
maxdistance=float: The maximum distance to consider when finding the horizon height
color_source=string: Source raster for colorization; Input and color_input are taken from input and color_input options respectively. The rest is computed using r.slope.aspect; Options: input, color_input, slope, aspect, dxy; Default: input; input: use the raster from the input option; color_input: use the raster from the color_input option; slope: compute and use slope; aspect: compute and use aspect; dxy: compute and use second order partial derivative dxy
color_input=name: Custom raster map to be used for colorization
color_table=string: Color table for colorization raster (preset color table by default); If empty, the color table of the created raster is used (not used at all for input and color_input); Options: reds, blues, greens, oranges, sepia, aspectcolr
colorized_output=name: Colorized sky-view factor
basename=string: Set the basename for the intermediate maps
nprocs=integer: Number of threads for parallel computing; 0: use OpenMP default; >0: use nprocs; <0: use MAX-nprocs; Default: 0
memory=memory in MB: Maximum memory to be used (in MB); Cache size for raster rows; Default: 300

DESCRIPTION
NOTES
EXAMPLES
SEE ALSO
REFERENCES
AUTHOR

DESCRIPTION

Module r.skyview computes skyview factor, a relief visualization technique (Zaksek et al. 2011). The value of each cell is given by the portion of visible sky (from that cell) limited by the surrounding relief. The values range from 0 to 1. The lighter the value is, the more open the terrain is.

When flag -o is set, r.skyview computes openness instead of skyview factor. Openness (based on positive openness by Yokoyama et al. 2002) takes into account zenith angles greater than 90 degrees, while skyview limits zenith angles to 90 degrees (celestial hemisphere). This makes difference for example for visualization of horizontal planes and slopes. Openness values range from 0 to 2.

NOTES

Module r.horizon is used to compute elevation angles.

EXAMPLES

We compute the skyview factor map of the North Carolina sample dataset elevation map:

g.region raster=elevation
r.skyview input=elevation output=elevation_skyview ndir=8

REFERENCES

Zaksek K, Ostir K, Kokalj Z. Sky-View Factor as a Relief Visualization Technique. Remote Sensing. 2011; 3(2):398-415.
Yokoyama R, Shirasawa M, Pike J R. Visualizing topography by Openness: A new application of image processing to digital elevation models. Photogrammetric engineering and remote sensing 68.3 (2002): 257-266.

AUTHOR

Anna Petrasova, NCSU GeoForAll

SOURCE CODE

Available at: r.skyview source code (history)

Latest change: Wednesday Jun 24 04:50:30 2026 in commit: 54496cff353fb9e64f8bda914e8eb6fe6a9b4f76