v.dissolve.html 2.4 KB

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  1. <h2>DESCRIPTION</h2>
  2. The <em>v.dissolve</em> module is used to merge adjacent areas in a vector
  3. map which share the same category value. The resulting merged area(s) retains
  4. this category value. Alternatively an integer or string column can be defined
  5. which is used to find adjacent polygons with identical attribute for common
  6. boundary dissolving. In this case the categories are not retained, only the
  7. values of the new key column. See the <em>v.reclass</em> help page for details.
  8. <h2>NOTES</h2>
  9. GRASS defines a vector area as composite entity consisting of a set of
  10. closed boundaries and a centroid. The centroids must contain a
  11. category number
  12. (see <em>v.centroids</em>), this number is linked to area attributes and
  13. database links.
  14. <p>
  15. Multiple attributes may be linked to a single vector entity through
  16. numbered fields referred to as layers. Refer to <em>v.category</em> for
  17. more details.
  18. <p>
  19. Merging of areas can also be accomplished using
  20. <tt>v.extract -d</tt> which provides some additional options.
  21. In fact, <em>v.dissolve</em> is simply a
  22. front-end to that module. The use of the <em>column</em> parameter
  23. adds a call to <em>v.reclass</em> before.
  24. <h2>EXAMPLES</h2>
  25. <h3>Basic use</h3>
  26. <div class="code"><pre>
  27. v.dissolve input=undissolved output=dissolved
  28. </pre></div>
  29. <h3>Dissolving based on column attributes</h3>
  30. North Carolina data set:
  31. <div class="code"><pre>
  32. g.copy vect=soils_general,mysoils_general
  33. v.dissolve mysoils_general output=mysoils_general_families column=GSL_NAME
  34. </pre></div>
  35. <h3>Dissolving adjacent SHAPE files to remove tile boundaries</h3>
  36. If tile boundaries of adjacent maps (e.g. CORINE Landcover SHAPE files)
  37. have to be removed, an extra step is required to remove duplicated
  38. boundaries:
  39. <div class="code"><pre>
  40. # patch tiles after import:
  41. v.patch -e `g.mlist type=vect pat="clc2000_*" fs=","` out=clc2000_patched
  42. # remove duplicated tile boundaries:
  43. v.clean clc2000_patched out=clc2000_clean tool=snap,break,rmdupl thresh=.01
  44. # dissolve based on column attributes:
  45. v.dissolve input=clc2000_clean output=clc2000_final col=CODE_00
  46. </pre></div>
  47. <h2>SEE ALSO</h2>
  48. <em>
  49. <a href="v.category.html">v.category</a>,
  50. <a href="v.centroids.html">v.centroids</a>,
  51. <a href="v.extract.html">v.extract</a>,
  52. <a href="v.reclass.html">v.reclass</a>
  53. </em>
  54. <h2>AUTHORS</h2>
  55. module: M. Hamish Bowman, Dept. Marine Science, Otago University, New Zealand<br>
  56. Markus Neteler for column support<br>
  57. help page: Trevor Wiens
  58. <p>
  59. <i>Last changed: $Date$</i>