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NAME

d.polar

DESCRIPTION

d.polar calculates and displays a polar diagram of an angle raster map such as aspect, wind direction, or flow.

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 points into the prevalent direction of the angles, its length is defined by the power of this direction.

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 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
Polar diagram of aspect map

SEE ALSO

d.histogram, r.slope.aspect

REQUIREMENT

The module needs xgraph to be installed. Probably d.graph should be used instead.

AUTHOR

Markus Neteler, ITC-irst

Last changed: $Date: 2006/03/01 05:07:57 $


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