Note: This addon document is for an older version of GRASS GIS that will be discontinued soon. You should upgrade your GRASS GIS installation, and read the current addon manual page.
NAME
r.skyview - Computes skyview factor visualization technique.
KEYWORDS
raster,
visualization
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] [--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
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.
Module
r.horizon is used to compute elevation angles.
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
r.horizon,
r.relief,
r.shaded.pca,
r.local.relief
- 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.
Anna Petrasova,
NCSU GeoForAll
SOURCE CODE
Available at:
r.skyview source code
(history)
Latest change: Mon Jun 28 07:54:09 2021 in commit: 1cfc0af029a35a5d6c7dae5ca7204d0eb85dbc55
Note: This addon document is for an older version of GRASS GIS that will be discontinued soon. You should upgrade your GRASS GIS installation, and read the current addon manual page.
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GRASS Development Team,
GRASS GIS 7.8.8dev Reference Manual