Path: news.mathworks.com!newsfeed-00.mathworks.com!newsfeed2.dallas1.level3.net!news.level3.com!postnews.google.com!i31g2000vbt.googlegroups.com!not-for-mail From: Rune Allnor <allnor@tele.ntnu.no> Newsgroups: comp.soft-sys.matlab Subject: Re: find distance along complicated geometric surface Date: Tue, 18 May 2010 11:52:48 -0700 (PDT) Organization: http://groups.google.com Lines: 28 Message-ID: <675156be-e00f-41cb-94cb-6daa88fad412@i31g2000vbt.googlegroups.com> References: <hss9t2$8ue$1@fred.mathworks.com> <99c70f0a-1227-4506-b3a1-ab85568616c8@l6g2000vbo.googlegroups.com> <hsuk28$b74$1@fred.mathworks.com> NNTP-Posting-Host: 77.19.84.113 Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 X-Trace: posting.google.com 1274208768 29804 127.0.0.1 (18 May 2010 18:52:48 GMT) X-Complaints-To: groups-abuse@google.com NNTP-Posting-Date: Tue, 18 May 2010 18:52:48 +0000 (UTC) Complaints-To: groups-abuse@google.com Injection-Info: i31g2000vbt.googlegroups.com; posting-host=77.19.84.113; posting-account=VAp5gAkAAAAmkCze5hvZtMeedpZWNthI User-Agent: G2/1.0 X-HTTP-UserAgent: Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 5.1; Trident/4.0; .NET CLR 2.0.50727; .NET CLR 3.0.04506.648; .NET CLR 3.5.21022; .NET CLR 3.0.4506.2152; .NET CLR 3.5.30729; .NET CLR 1.1.4322),gzip(gfe) Xref: news.mathworks.com comp.soft-sys.matlab:636979 On 18 Mai, 19:51, "Matt J " <mattjacREM...@THISieee.spam> wrote: > Rune Allnor <all...@tele.ntnu.no> wrote in message <99c70f0a-1227-4506-b3a1-ab8556861...@l6g2000vbo.googlegroups.com>... > > The *idea* is simple, assuming you already have a surface > > consisting of edges and vertices, like in a triangulation: > > Track the points where you cross edges, and compute the > > distance between consecutive edge crossings (possibly also > > accounting for path waypoints). The total distance along the > > path will be the cumulant sum of all such edge-to-edge > > distances. > > ======== > > The difficulty though, Rune, is that you don't have the shortest-distance path a priori. It's finding the shortest path, not computing its length, which is the challenge. I can't see how being able to compute the distance along a genrral path isn't helpful: 1) Select an initial path 2) Compute the distance along this path 3) Modify the path in a way that likely might shorten the distance 4) Repeat from 2 until no significant improvements in path distance can be made. Of course, one can only hope to find a local solution to this problem. Rune