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

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=nameA [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)

       Main index | Display index | Topics index | Keywords index |  Graphical
       index | Full index

       A(C) 2003-2020 GRASS Development	Team, GRASS GIS	7.8.3 Reference	Manual

GRASS 7.8.3							    d.polar(1)

NAME | KEYWORDS | SYNOPSIS | DESCRIPTION | NOTES | EXAMPLE | SEE ALSO | XGRAPH REQUIREMENT | REFERENCES | AUTHORS | SOURCE CODE

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