d.polar(1)

1d.polar(1)                    Grass 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
7       directions
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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]   [eps=string]
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17   Flags:
18       -x  Plot using Xgraph
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20   Parameters:
21       map=name
22           Name of raster angle map
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24       undef=float
25           Pixel value to be interpreted as undefined (different from NULL)
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27       eps=string
28           Name of optional EPS output file
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DESCRIPTION

31       d.polar calculates and displays a polar diagram of an angle raster  map
32       such  as aspect, wind direction, or flow.  The input angle map orienta‐
33       tion must be counter-clockwise (CCW) from east, and the angle map units
34       must  be  degrees.  This  refers  to  the standard orientation of GRASS
35       (e.g., see r.slope.aspect).
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37       The radius of the outer circle is defined by the total number of pixels
38       in  the  map.  If the polar diagram does not reach the outer circle, no
39       data (NULL) pixels were found in the map.
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41       The vector in the diagram indicates a prevailing direction, its  length
42       the  strength of such direction. In case all angle vectors are oriented
43       along the same direction, the length for the vector is maximal (in fact
44       it  is equal to length of the most populated bin of the underlying his‐
45       togram).
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47       As a side effect, the quality of the angle map can be derived from  the
48       diagram.  Strong  spikes  may  indicate  an  over-representation of the
49       related angle(s) which happens in particular if integer maps are used.
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NOTES

52       If the eps parameter is used, the diagram is generated as EPS file.  If
53       the  -x  flag  is  used  xgraph is lauched.  Otherwise d.polar will use
54       d.graph to draw the plot in the current display frame.
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56       If d.polar is used on an aspect map generated  by  r.slope.aspect,  the
57       undef  parameter should be set to 0 to distinguish NO DATA (NULL) areas
58       from areas where aspect is undefined (i.e. flat areas).
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60       Polar diagram of aspect map
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EXAMPLE

63       In this example, the polar diagram of the 'aspect'  angle  map  in  the
64       Spearfish location is generated:
65       d.polar aspect
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XGRAPH REQUIREMENT

72       Xgraph must be installed for the -x flag to function.
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AUTHORS

75       Markus Neteler, ITC-irst, Italy
76       Bruno Caprile, ITC-irst, Italy
77       Hamish Bowman, Otago University, New Zealand
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79       Last changed: $Date: 2007/03/08 13:51:30 $
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81       Full index
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85GRASS 6.2.2                                                         d.polar(1)