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r.lfp.html
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<h2>DESCRIPTION</h2>
<em>r.lfp</em> calculates the longest flow path for a given outlet point and
creates a new raster map with a thin line representing the longest flow path.
This module requires the <em>r.stream.distance</em> addon.
<h2>NOTES</h2>
<em>r.lfp</em> creates a longest flow path raster map using a drainage
direction raster map and the coordinates of an outlet point. The module
internally runs <em>r.stream.distance</em> twice to calculate flow length
downstream and upstream raster maps, and combines them to get the longest flow
path. An input drainage map can be created using <em>r.watershed</em> or
<em>r.stream.extract</em>.
<h2>EXAMPLES</h2>
<h3>Workflow example</h3>
<div class="code"><pre>
r.watershed elevation=elev drainage=drain
r.water.outlet input=drain output=basin coordinates=-888857.11,1117788.38
r.lfp input=drain output=lfp coordinates=-888857.11,1117788.38
</pre></div>
<h3>North Carolina sample dataset example</h3>
<div class="code"><pre>
# set computational region
g.region raster=elevation -p
# calculate drainage directions
r.watershed elevation=elevation drainage=drain_directions
# calculate outlet point related watershed
r.water.outlet input=drain_directions output=basin coordinates=642455,222614
# calculate longest flow path
r.lfp input=drain_directions output=lfp coordinates=642455,222614
</pre></div>
<img src="r_lfp_nc_example.png">
<h2>SEE ALSO</h2>
<em>
<a href="v.lfp.html">v.lfp</a>,
<a href="r.watershed.html">r.watershed</a>,
<a href="r.stream.extract.html">r.stream.extract</a>,
<a href="r.stream.distance.html">r.stream.distance</a>
</em>
<br>
<a href="http://idea.isnew.info/how-to-calculate-the-longest-flow-path-in-grass-gis.html">How to calculate the longest flow path in GRASS GIS</a>
<h2>AUTHOR</h2>
<a href="mailto:grass4u@gmail com">Huidae Cho</a>
<p><i>Last changed: $Date: 2017-03-11 01:31:12 -0500 (Sat, 11 Mar 2017) $</i>