[mkgmap-dev] Simplifying ways
From Felix Hartmann extremecarver at googlemail.com on Sat Nov 28 22:01:48 GMT 2009
Mark Burton wrote: > Hi Felix (cc Johann) > > >> Just as a follow up, I noticed that the v8 patch (simplify ...) - >> actually routing over long distances in Mapsource became worse. Some >> routes I can calculate without using this patch, don't calculate with >> the patch anymore. >> > > You posted this comment with a subject line related to "remove bogus > nodes" but I guess you're really talking about the latest patch from > Johann. > No Johanns (v8) patch actually improves long distance routing (2-3 additional turns), while the remove bogus roads makes long distance routing worse for me (3-4 turns less). Sorry for the wrong text. I have no clue why the remove bogus nodes makes routing worse. v3 actually is great insofar as it allows several routable roads with different speed, but so far I have not been able to make such ways opposing oneways - but they are different speed. Currently playing around to find out how I can trick it into two opposing oneways (while the oneway is "artificial" in both directions in so far that I use incomplete rules to set it up). > If you're saying that with that patch some long distance routing is > broken it doesn't surprise me. I haven't looked at the patch in detail > but my initial impression is that it can't work because it joins up > line segments that "belong" to different roads. Here's my reasoning: > > Basically, each routable road generates 2 data items: > > 1 - the routing data (nodes and arcs used to calculate routes) > > 2 - the graphical line data (what you see on the screen) > > So if a route across the country uses, say, 4 different roads (for > this discussion assume the roads just connect one end to the other > without side roads) then there will be 4 arcs in the route. On the > screen, the line segments for the 4 roads will be displayed. There is a > one-to-one correspondence between the displayed lines and the > underlying routing arcs. In fact, there is a real linkage between the > line data and the routing info. > > The simplify patch in it's current form reduces the number of drawn > lines by merging the graphical line data. It doesn't (unless I am > mistaken) merge the routing information. So now there is no-longer a > one-to-one correspondence between the displayed line(s) and the > underlying routing arcs. > > Imagine that in our 4 road route, the 3 following roads are merged > into the first. So now we have 1 graphical entity but we still have 4 > arcs. The linkage from the remaining line relates to the 1st arc only > even though the graphical line spans the whole route. > > As I said, I haven't studied the patch in detail. I could be wrong. > > Cheers, > > Mark > _______________________________________________ > mkgmap-dev mailing list > mkgmap-dev at lists.mkgmap.org.uk > http://www.mkgmap.org.uk/mailman/listinfo/mkgmap-dev > -------------- next part -------------- An HTML attachment was scrubbed... URL: http://lists.mkgmap.org.uk/pipermail/mkgmap-dev/attachments/20091128/58b90c14/attachment.html
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