d.polar(1grass) GRASS GIS User's Manual d.polar(1grass)
NAME
d.polar - Draws polar diagram of angle map such as aspect or flow di-
rections
KEYWORDS
display, diagram
SYNOPSIS
d.polar
d.polar --help
d.polar [-x] map=name [undef=float] [output=name] [--overwrite]
[--help] [--verbose] [--quiet] [--ui]
Flags:
-x
Plot using Xgraph
--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:
map=name [required]
Name of raster angle map
undef=float
Pixel value to be interpreted as undefined (different from NULL)
output=name
Name for optional EPS output file
DESCRIPTION
d.polar calculates and displays a polar diagram of an angle raster map
such as aspect, wind direction, or flow. The input angle map orienta-
tion must be counter-clockwise (CCW) from east, and the angle map units
must be degrees. This refers to the standard orientation of GRASS
(e.g., see r.slope.aspect).
The radius of the outer circle is defined by the total number of pixels
in the map. If the polar diagram does not reach the outer circle, no
data (NULL) pixels were found in the map.
The vector in the diagram indicates a prevailing direction, its length
the strength of such direction. In case all angle vectors are oriented
along the same direction, the length for the vector is maximal (in fact
it is equal to length of the most populated bin of the underlying his-
togram).
As a side effect, the quality of the angle map can be derived from the
diagram. Strong spikes may indicate an over-representation of the re-
lated angle(s) which happens in particular if integer maps are used.
NOTES
If the output parameter is used, the diagram is generated as EPS file.
If the -x flag is used xgraph is launched. Otherwise d.polar will use
d.graph to draw the plot in the current display frame.
If d.polar is used on an aspect map generated by r.slope.aspect, the
undef parameter should be set to 0 to distinguish NO DATA (NULL) areas
from areas where aspect is undefined (i.e. flat areas).
Polar diagram of aspect map
EXAMPLE
In this example, the polar diagram of the ’aspect’ angle map in the
North Carolina sample dataset location is generated:
g.region raster=aspect -p
d.polar aspect
SEE ALSO
d.graph, d.histogram, d.rast.arrow, r.slope.aspect
XGRAPH REQUIREMENT
Xgraph must be installed for the -x flag to function.
REFERENCES
J. Hofierka, H. Mitasova, and M. Neteler (2009): Terrain parameteriza-
tion in GRASS. In T. Hengl and H.I. Reuter, editors, Geomorphometry:
concepts, software, applications. Elsevier (DOI)
AUTHORS
Markus Neteler, ITC-irst, Italy
Bruno Caprile, ITC-irst, Italy
Hamish Bowman, Otago University, New Zealand
SOURCE CODE
Available at: d.polar source code (history)
Accessed: unknown
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GRASS 7.8.7 d.polar(1grass)
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