1d.polar(1)                  GRASS GIS User's Manual                 d.polar(1)
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NAME

6       d.polar   - Draws polar diagram of angle map such as aspect or flow di‐
7       rections
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KEYWORDS

10       display, diagram
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SYNOPSIS

13       d.polar
14       d.polar --help
15       d.polar [-x] map=name   [undef=float]    [output=name]    [--overwrite]
16       [--help]  [--verbose]  [--quiet]  [--ui]
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18   Flags:
19       -x
20           Plot using Xgraph
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22       --overwrite
23           Allow output files to overwrite existing files
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25       --help
26           Print usage summary
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28       --verbose
29           Verbose module output
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31       --quiet
32           Quiet module output
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34       --ui
35           Force launching GUI dialog
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37   Parameters:
38       map=name [required]
39           Name of raster angle map
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41       undef=float
42           Pixel value to be interpreted as undefined (different from NULL)
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44       output=name
45           Name for optional EPS output file
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DESCRIPTION

48       d.polar  calculates and displays a polar diagram of an angle raster map
49       such as aspect, wind direction, or flow.  The input angle map  orienta‐
50       tion must be counter-clockwise (CCW) from east, and the angle map units
51       must be degrees. This refers  to  the  standard  orientation  of  GRASS
52       (e.g., see r.slope.aspect).
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54       The radius of the outer circle is defined by the total number of pixels
55       in the map. If the polar diagram does not reach the  outer  circle,  no
56       data (NULL) pixels were found in the map.
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58       The  vector in the diagram indicates a prevailing direction, its length
59       the strength of such direction. In case all angle vectors are  oriented
60       along the same direction, the length for the vector is maximal (in fact
61       it is equal to length of the most populated bin of the underlying  his‐
62       togram).
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64       As  a side effect, the quality of the angle map can be derived from the
65       diagram. Strong spikes may indicate an over-representation of  the  re‐
66       lated angle(s) which happens in particular if integer maps are used.
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NOTES

69       If  the output parameter is used, the diagram is generated as EPS file.
70       If the -x flag is used xgraph is launched.  Otherwise d.polar will  use
71       d.graph to draw the plot in the current display frame.
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73       If  d.polar  is  used on an aspect map generated by r.slope.aspect, the
74       undef parameter should be set to 0 to distinguish NO DATA (NULL)  areas
75       from areas where aspect is undefined (i.e. flat areas).
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77       Polar diagram of aspect map
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EXAMPLE

80       In  this  example,  the  polar diagram of the ’aspect’ angle map in the
81       North Carolina sample dataset location is generated:
82       g.region raster=aspect -p
83       d.polar aspect
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XGRAPH REQUIREMENT

86       Xgraph must be installed for the -x flag to function.
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SEE ALSO

89        d.graph, d.histogram, d.rast.arrow, r.slope.aspect
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REFERENCES

92       J. Hofierka, H. Mitasova, and M. Neteler (2009): Terrain  parameteriza‐
93       tion  in  GRASS.  In T. Hengl and H.I. Reuter, editors, Geomorphometry:
94       concepts, software, applications. Elsevier (DOI)
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AUTHORS

97       Markus Neteler, ITC-irst, Italy
98       Bruno Caprile, ITC-irst, Italy
99       Hamish Bowman, Otago University, New Zealand
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SOURCE CODE

102       Available at: d.polar source code (history)
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104       Accessed: Saturday Jan 21 20:40:59 2023
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106       Main index | Display index | Topics index | Keywords index |  Graphical
107       index | Full index
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109       © 2003-2023 GRASS Development Team, GRASS GIS 8.2.1 Reference Manual
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113GRASS 8.2.1                                                         d.polar(1)