[GRASS-SVN] r38196 - grass-addons/raster/r.denoise

[svn_grass at osgeo.org]

Author: stevensj
Date: 2009-07-03 13:00:11 -0400 (Fri, 03 Jul 2009)
New Revision: 38196

Added:
   grass-addons/raster/r.denoise/description.html
Log:
Renamed instructions page

Added: grass-addons/raster/r.denoise/description.html
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--- grass-addons/raster/r.denoise/description.html	                        (rev 0)
+++ grass-addons/raster/r.denoise/description.html	2009-07-03 17:00:11 UTC (rev 38196)
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+<h2>REQUIREMENTS</h2>
+<em><b>r.denoise</em></b> requires that <em>mdenoise</em>, the executable version of Sun et al.'s (2007) denoising algorithm, is available on the $PATH.  <em>mdenoise</em> can be compiled and installed as follows:
+
+<div class="code"><pre>
+wget http://www.cs.cf.ac.uk/meshfiltering/index_files/Doc/mdsource.zip
+unzip mdsource.zip
+cd mdenoise
+g++ -o mdenoise mdenoise.cpp triangle.c
+ln -s `pwd`/mdenoise /some/directory/on/the/$PATH
+</pre></div>
+
+<h2>DESCRIPTION</h2>
+
+<p>
+Sun et al.'s (2007) <a href="http://www.cs.cf.ac.uk/meshfiltering/index_files/Page342.htm">denoising algorithm</a> is a feature-preserving mesh denoising algorithm that smooths the surfaces of computer models of three dimensional objects such as those used in computer-aided design and graphics.  It removes random noise while preserving sharp features and smoothing with minimal changes to the original data. <em>r.denoise</em> is a UNIX shell script that allows the algorithm to be run on DEMs from within <em>GRASS</em>.  Denoising DEMs can improve clarity and quality of derived products such as slope and hydraulic maps.
+<p>
+The amount of smoothing is controlled by the <em>threshold</em> and <em>iterations</em> parameters.  Increasing the <em>threshold</em> decreases how sharp a feature needs to be to be preserved e.g. decreases the smoothing.  To preserve ridge crests in mountain areas, T > 0.9 is recommended. Setting T too high results in the preservation of noise.  For SRTM data, which is already partly smoothed by NASA, T = 0.99 can be used.  Increasing the number of <em>iterations</em> increases the smoothing and the range of spatial correlation of the output dataset.  A small number, e.g. 5 or fewer, typically gives the best results.  See the REFERENCES for more detailed information.
+
+<h2>NOTES</h2>
+<p>
+<em>r.denoise</em> works with a cartesian coordinate system.  Thus data in geographic (lat-long) coordinates require projection during processing.  The script is able to do this if the <a href="http://www.epsg-registry.org/">EPSG code</a> of a suitable coordinate system is provided.
+
+<h2>REFERENCES</h2>
+<ul>
+	<li>For further information on denoising DEMs, see: <a href="http://personalpages.manchester.ac.uk/staff/john.stevenson/mdenoise">Using Sun's denoising algorithm on topographic data</a>.
+	<li>Sun X, Rosin PL, Martin RR, Langbein FC (2007) Fast and Effective Feature-Preserving Mesh Denoising. IEEE Transactions on Visualisation and Computer Graphics, 13(5):925-938</li>
+	<li>Stevenson JA, Sun X, Mitchell NC. Despeckling SRTM and other topographic data with a denoising algorithm. In review: Geomorphology.</li>
+</ul>
+
+<H2>SEE ALSO</H2>
+<EM>
+<A HREF="r.stats.html">r.stats</A>,
+<A HREF="r.in.xyz.html">r.in.xyz</A>,
+<A HREF="r.neighbors.html">r.neighbors</A>,
+<A HREF="r.topidx.html">r.topidx</A>,
+</EM>
+
+<H2>AUTHOR</H2>
+John A Stevenson - Manchester University<br><br>
+The module was written as part of a project funded by <A href="http://www.epsrc.ac.uk">EPSRC</A> Grant no. EP/C007972/1 (P.I. Paul Rosin, Cardiff University).
+
+<p>
+<i>Last changed: $Date: 2009-07-03 07:58:42 +0100 (Fri, 03 Jul 2009) $</i>