NAME¶

d.polar - Draws polar diagram of angle map such as aspect or flow directions

KEYWORDS¶

display, diagram

SYNOPSIS¶

d.polar d.polar help d.polar [-x] map=name [undef=float] [eps=string] [--verbose] [--quiet]

Flags:¶

-x

 

Plot using Xgraph

--verbose

 

Verbose module output

--quiet

 

Quiet module output

Parameters:¶

map=name

 

Name of raster angle map

undef=float

 

Pixel value to be interpreted as undefined (different from NULL)

eps=string

 

Name of 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 orientation 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 histogram). 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 related angle(s) which happens in particular if integer maps are used.

NOTES¶

If the eps parameter is used, the diagram is generated as EPS file. If the -x flag is used xgraph is lauched. 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 rast=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.

REFERENCE¶

J. Hofierka, H. Mitasova, and M. Neteler (2009): Terrain parameterization 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 Last changed: $Date: 2011-11-08 12:29:50 +0100 (Tue, 08 Nov 2011) $ Full index © 2003-2014 GRASS Development Team