<html><head></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><div>One of my students was having problems with r.walk not properly reflecting surface topography in 6.4.2 svn (from a few weeks ago).</div><div><br></div><div>So I checked it out today. My comparison is not quite the same as hers as she is on Mac OS X 10.6.8 and I've tested this on 10.7.2 (Lion). But we're using the same GRASS builds (done with 10.6.8 on my other computer).</div><div><br></div><div>I did not have the same problem she did. I tested with the Spearfish demo set. She is using a DEM in a Lambert Conformal Conic projection (which I suppose might be a problem for some reason).</div><div><br></div><div>However, I did turn up something of interest for the upcoming GRASS 6.4.2 release. </div><div><br></div><div>In 6.4.1, we did not include the new backlink map option, but I thought it was going to be in 6.4.2. So far it has not been backported from 6.5.</div><div><br></div><div>Also, running r.walk without the backlink in GRASS 6.4.2 and GRASS 7 produces significantly different results. Here are the links to a couple of outputs of a difference map between r.walk on 6.4.2 minus r.walk on GRASS 7 using exactly the same command and files.</div><div><br></div><div><div>r.walk elevation="elevation.dem@PERMANENT" friction="flat1m@PERMANENT" output="cost1" start_points="Elkhorn_Peak_site@G7_vector" max_cost=0 percent_memory=100 walk_coeff="0.72,6.0,1.9998,-1.9998" lambda=1.0 slope_factor=-0.2125 </div></div><div><br></div><div><a href="http://dl.dropbox.com/u/7437464/rwalk_diff.jpg">http://dl.dropbox.com/u/7437464/rwalk_diff.jpg</a></div><div><a href="http://dl.dropbox.com/u/7437464/rwalk_diff_histogram.png">http://dl.dropbox.com/u/7437464/rwalk_diff_histogram.png</a></div><div><br></div>As you can see, there are very patterned differences in the behavior of r.walk between the 2 GRASS versions. The differences are not huge (in the range of +3 to -13 minutes), but are still notable. Beyond adding the backlink option, do the r.walk algorithms differ significantly between them?<div><br></div><div>Also, has anybody had any problems with r.walk in a Lambert projection?<br><div><br></div><div>Michael<br><div><div>
<div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><span class="Apple-style-span" style="border-collapse: separate; color: rgb(0, 0, 0); font-family: Helvetica; font-size: medium; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-border-horizontal-spacing: 0px; -webkit-border-vertical-spacing: 0px; -webkit-text-decorations-in-effect: none; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px; "><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><span class="Apple-style-span" style="border-collapse: separate; color: rgb(0, 0, 0); font-family: Helvetica; font-size: medium; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-border-horizontal-spacing: 0px; -webkit-border-vertical-spacing: 0px; -webkit-text-decorations-in-effect: none; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px; "><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><span class="Apple-style-span" style="border-collapse: separate; color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-border-horizontal-spacing: 0px; -webkit-border-vertical-spacing: 0px; -webkit-text-decorations-in-effect: none; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px; "><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><div><div><div>____________________</div><div>C. Michael Barton</div><div>Director, Center for Social Dynamics & Complexity </div><div>Professor of Anthropology, School of Human Evolution & Social Change</div><div>Arizona State University</div><div><br></div>voice: <span class="Apple-tab-span" style="white-space: pre; "> </span>480-965-6262 (SHESC), 480-727-9746 (CSDC)<br>fax: 480-965-7671 (SHESC), 480-727-0709 (CSDC)<br><div>www: <a href="http://www.public.asu.edu/~cmbarton">http://www.public.asu.edu/~cmbarton</a>, <a href="http://csdc.asu.edu">http://csdc.asu.edu</a></div><br></div></div><br></div></span><br class="Apple-interchange-newline"></div></span><br class="Apple-interchange-newline"></div></span><br class="Apple-interchange-newline"></div><br class="Apple-interchange-newline"></div><br class="Apple-interchange-newline"></div><br class="Apple-interchange-newline"></div><br class="Apple-interchange-newline"><br class="Apple-interchange-newline">
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