r.skyview

Computes skyview factor visualization technique.

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] [--overwrite] [--verbose] [--quiet] [--qq] [--ui]

Example:

r.skyview input=name output=name ndir=16

grass.script.run_command("r.skyview", input, output, ndir=16, maxdistance=None, color_source="input", color_input=None, color_table=None, colorized_output=None, basename=None, flags=None, overwrite=False, verbose=False, quiet=False, superquiet=False)

Example:

gs.run_command("r.skyview", input="name", output="name", ndir=16)

Parameters

Command linePython (grass.script)

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)
    Allowed values: 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
    Allowed values: 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)
    Allowed values: reds, blues, greens, oranges, sepia, aspectcolr
colorized_output=name
    Colorized sky-view factor
basename=string
    Set the basename for the intermediate maps
-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
--qq
    Very quiet module output
--ui
    Force launching GUI dialog

input : str, required
    Name of input raster map
    Used as: input, raster, name
output : str, required
    Name for output raster map
    Used as: output, raster, name
ndir : int, required
    Number of directions (8 to 32 recommended)
    Allowed values: 2-360
    Default: 16
maxdistance : float, optional
    The maximum distance to consider when finding the horizon height
color_source : str, optional
    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
    Allowed values: input, color_input, slope, aspect, dxy
    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
    Default: input
color_input : str, optional
    Custom raster map to be used for colorization
    Used as: input, raster, name
color_table : str, optional
    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)
    Allowed values: reds, blues, greens, oranges, sepia, aspectcolr
colorized_output : str, optional
    Colorized sky-view factor
    Used as: output, raster, name
basename : str, optional
    Set the basename for the intermediate maps
flags : str, optional
    Allowed values: o, n
    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: bool, optional
    Allow output files to overwrite existing files
    Default: False
verbose: bool, optional
    Verbose module output
    Default: False
quiet: bool, optional
    Quiet module output
    Default: False
superquiet: bool, optional
    Very quiet module output
    Default: False

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: Friday Feb 21 10:10:05 2025 in commit 7d78fe3