<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> <html> <head> <title>GRASS GIS: d.polar</title> <meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1"> <link rel="stylesheet" href="grassdocs.css" type="text/css"> </head> <body bgcolor="white"> <img src="grass_logo.png" alt="GRASS logo"><hr align=center size=6 noshade> <h2>NAME</h2> <em><b>d.polar</b></em> - Draws polar diagram of angle map such as aspect or flow directions <h2>KEYWORDS</h2> display, diagram <h2>SYNOPSIS</h2> <b>d.polar</b><br> <b>d.polar help</b><br> <b>d.polar</b> [-<b>x</b>] <b>map</b>=<em>name</em> [<b>undef</b>=<em>float</em>] [<b>eps</b>=<em>string</em>] [--<b>verbose</b>] [--<b>quiet</b>] <h3>Flags:</h3> <DL> <DT><b>-x</b></DT> <DD>Plot using Xgraph</DD> <DT><b>--verbose</b></DT> <DD>Verbose module output</DD> <DT><b>--quiet</b></DT> <DD>Quiet module output</DD> </DL> <h3>Parameters:</h3> <DL> <DT><b>map</b>=<em>name</em></DT> <DD>Name of raster angle map</DD> <DT><b>undef</b>=<em>float</em></DT> <DD>Pixel value to be interpreted as undefined (different from NULL)</DD> <DT><b>eps</b>=<em>string</em></DT> <DD>Name of optional EPS output file</DD> </DL> <H2>DESCRIPTION</H2> <EM>d.polar</EM> 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 <em>r.slope.aspect</em>). <P> 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. <P> 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). <P> 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. <H2>NOTES</H2> If the <b>eps</b> parameter is used, the diagram is generated as EPS file. If the <b>-x</b> flag is used <EM>xgraph</EM> is lauched. Otherwise <em>d.polar</em> will use <em>d.graph</em> to draw the plot in the current display frame. <P> If <EM>d.polar</EM> is used on an aspect map generated by <EM>r.slope.aspect</EM>, the <b>undef</b> parameter should be set to 0 to distinguish NO DATA (NULL) areas from areas where aspect is undefined (i.e. flat areas). <P> <center> <img src="d_polar_aspect.png" alt="Polar diagram of aspect map"> <BR> <i>Polar diagram of aspect map</i> </center> <h2>EXAMPLE</h2> In this example, the polar diagram of the 'aspect' angle map in the Spearfish location is generated: <div class="code"><pre> d.polar aspect </pre></div> <H2>SEE ALSO</H2> <EM><A HREF="d.graph.html">d.graph</A></EM>, <EM><A HREF="d.histogram.html">d.histogram</A></EM>, <EM><A HREF="d.rast.arrow.html">d.rast.arrow</A></EM>, <EM><A HREF="r.slope.aspect.html">r.slope.aspect</A></EM> <H2>XGRAPH REQUIREMENT</H2> <A HREF="http://www.xgraph.org">Xgraph</a> must be installed for the <b>-x</b> flag to function. <H2>AUTHORS</H2> Markus Neteler, ITC-irst, Italy<BR> Bruno Caprile, ITC-irst, Italy<BR> Hamish Bowman, Otago University, New Zealand<BR> <p><i>Last changed: $Date: 2006-10-30 14:34:00 +0100 (Mon, 30 Oct 2006) $</i></p> <HR> <P><a href="index.html">Main index</a> - <a href="display.html">display index</a> - <a href="full_index.html">Full index</a></P> <P>© 2003-2008 <a href="http://grass.osgeo.org">GRASS Development Team</a></p> </body> </html>
