[GRASS-SVN] r64847 - grass/branches/releasebranch_7_0/raster/r.walk
svn_grass at osgeo.org
svn_grass at osgeo.org
Thu Mar 12 19:21:15 PDT 2015
Author: annakrat
Date: 2015-03-12 19:21:15 -0700 (Thu, 12 Mar 2015)
New Revision: 64847
Modified:
grass/branches/releasebranch_7_0/raster/r.walk/r.walk.html
Log:
r.walk: explain coefficients and friction in manual (merge from trunk, r64846)
Modified: grass/branches/releasebranch_7_0/raster/r.walk/r.walk.html
===================================================================
--- grass/branches/releasebranch_7_0/raster/r.walk/r.walk.html 2015-03-13 02:19:17 UTC (rev 64846)
+++ grass/branches/releasebranch_7_0/raster/r.walk/r.walk.html 2015-03-13 02:21:15 UTC (rev 64847)
@@ -7,7 +7,7 @@
<p>
<em>r.walk</em> outputs 1) a raster map showing the lowest
-cumulative cost of moving between each cell and the user-specified
+cumulative cost (time) of moving between each cell and the user-specified
starting points and 2) a second raster map showing the movement
direction to the next cell on the path back to the start point (see
<a href="#move">Movement Direction</a>). It uses an input elevation
@@ -29,14 +29,14 @@
specific slope intervals:
<div class="code"><pre>
-T= [(a)*(Delta S)] + [(b)*(Delta H uphill)] + [(c)*(Delta H moderate downhill)] + [(d)*(Delta H steep downhill)]
+T = a*delta_S + b*delta_H_uphill + c*delta_H_moderate_downhill + d*delta_H_steep_downhill
</pre></div>
where:
<ul>
<li><tt>T</tt> is time of movement in seconds,</li>
- <li><tt>Delta S</tt> is the distance covered in meters,</li>
- <li><tt>Delta H</tt> is the altitude difference in meter.</li>
+ <li><tt>delta S</tt> is the horizontal distance covered in meters,</li>
+ <li><tt>delta H</tt> is the altitude difference in meters.</li>
</ul>
<p>
@@ -44,10 +44,13 @@
movement speed in the different conditions and are linked to:
<ul>
- <li>a: underfoot condition (a=1/walking_speed)</li>
- <li>b: underfoot condition and cost associated to movement uphill</li>
- <li>c: underfoot condition and cost associated to movement moderate downhill</li>
- <li>d: underfoot condition and cost associated to movement steep downhill</li>
+ <li>a: time in seconds it takes to walk for 1 meter a flat surface (1/walking speed)</li>
+ <li>b: additional walking time in seconds, per meter of elevation gain
+ on uphill slopes</li>
+ <li>c: additional walking time in seconds, per meter of elevation loss
+ on moderate downhill slopes (use positive value for decreasing cost)</li>
+ <li>d: additional walking time in seconds, per meter of elevation loss
+ on steep downhill slopes (use negative value for increasing cost)</li>
</ul>
It has been proved that moving downhill is favourable up to a specific
@@ -59,12 +62,14 @@
Langmuir (0.72, 6.0, 1.9998, -1.9998), based on man walking effort in
standard conditions.
-<p>The <b>lambda</b> parameter of the linear equation
-combining movement and friction costs:<br>
+<p>The <b>friction</b> cost parameter represents a time penalty in seconds
+of additional walking time to cross 1 meter distance.
+<p>The <b>lambda</b> parameter is a dimensionless scaling factor of the friction cost:
+
<div class="code"><pre>
-total cost = movement time cost + (lambda) * friction costs
+total cost = movement time cost + lambda * friction costs * delta_S
</pre></div>
-must be set in the option section of <em>r.walk</em>.
+
<p>
For a more accurate result, the "knight's move" option can be used
(although it is more time consuming). In the diagram below, the center
More information about the grass-commit
mailing list