d.polar.html 2.6 KB

12345678910111213141516171819202122232425262728293031323334353637383940414243444546474849505152535455565758596061626364656667686970717273747576777879
  1. <h2>DESCRIPTION</h2>
  2. <em>d.polar</em> calculates and displays a polar diagram of an
  3. angle raster map such as aspect, wind direction, or flow.
  4. The input angle map orientation must be counter-clockwise (CCW)
  5. from east, and the angle map units must be degrees. This refers
  6. to the standard orientation of GRASS (e.g., see <em>r.slope.aspect</em>).
  7. <p>The radius of the outer circle is defined by the total number
  8. of pixels in the map. If the polar diagram does not reach the
  9. outer circle, no data (NULL) pixels were found in the map.
  10. <p>The vector in the diagram indicates a prevailing direction, its length
  11. the strength of such direction. In case all angle vectors are oriented
  12. along the same direction, the length for the vector is maximal (in fact
  13. it is equal to length of the most populated bin of the underlying histogram).
  14. <p>As a side effect, the quality of the angle map can be derived from
  15. the diagram. Strong spikes may indicate an over-representation of
  16. the related angle(s) which happens in particular if integer maps
  17. are used.
  18. <h2>NOTES</h2>
  19. If the <b>output</b> parameter is used, the diagram is generated
  20. as EPS file. If the <b>-x</b> flag is used <em>xgraph</em> is launched.
  21. Otherwise <em>d.polar</em> will use <em>d.graph</em> to draw the plot
  22. in the current display frame.
  23. <p>If <em>d.polar</em> is used on an aspect map generated by
  24. <em>r.slope.aspect</em>, the <b>undef</b> parameter should be
  25. set to 0 to distinguish NO DATA (NULL) areas from areas where
  26. aspect is undefined (i.e. flat areas).
  27. <p>
  28. <center>
  29. <img src="d_polar_aspect.png" alt="Polar diagram of aspect map">
  30. <br>
  31. <i>Polar diagram of aspect map</i>
  32. </center>
  33. <h2>EXAMPLE</h2>
  34. In this example, the polar diagram of the 'aspect' angle map in the
  35. North Carolina sample dataset location is generated:
  36. <div class="code"><pre>
  37. g.region raster=aspect -p
  38. d.polar aspect
  39. </pre></div>
  40. <h2>SEE ALSO</h2>
  41. <em>
  42. <a href="d.graph.html">d.graph</a>,
  43. <a href="d.histogram.html">d.histogram</a>,
  44. <a href="d.rast.arrow.html">d.rast.arrow</a>,
  45. <a href="r.slope.aspect.html">r.slope.aspect</a>
  46. </em>
  47. <h2>XGRAPH REQUIREMENT</h2>
  48. <a href="http://www.xgraph.org">Xgraph</a> must be installed for the
  49. <b>-x</b> flag to function.
  50. <h2>REFERENCES</h2>
  51. J. Hofierka, H. Mitasova, and M. Neteler (2009): Terrain parameterization in GRASS.
  52. In T. Hengl and H.I. Reuter, editors, Geomorphometry: concepts, software, applications. Elsevier
  53. (<a href="http://dx.doi.org/10.1016/S0166-2481(08)00017-2">DOI</a>)
  54. <h2>AUTHORS</h2>
  55. Markus Neteler, ITC-irst, Italy<br>
  56. Bruno Caprile, ITC-irst, Italy<br>
  57. Hamish Bowman, Otago University, New Zealand<br>
  58. <!--
  59. <p>
  60. <i>Last changed: $Date$</i>
  61. -->