[mkgmap-dev] Commit: r1410: Add --merge-lines option to combine lines at lower zoom levels.From Felix Hartmann extremecarver at googlemail.com on Tue Dec 1 22:01:29 GMT 2009
On 01.12.2009 22:43, Mark Burton wrote: > Hi Johann, > > >> Hi Mark, >> >> if your guess is true (it indeed seems so), then this would mean that >> there is some linking between the graphical line and the arc. I know >> there is a one to one link at highest resolution. There seems to be link >> at lower resolutions too. >> >> This may well be the unknown reason for the improving of the routing >> with the merge-lines option. >> > Perhaps, but that is a mystery to me. > > >> What I do not understand: How can I link a long line to a lot of arcs. >> There must be a way, as the original garmin maps contains long lines >> too. Are there some arcs for lower resolutions too? >> > So far, I have not seen any evidence of that. > > What I have seen in some maps created by cgpsmapper is what I call > "short-circuit arcs". These are extra arcs that jump over some of the > points in the way to make a more direct route. Here's some ascii art > that illustrates what I mean: > > > ---------SCA--------- > | | > -----A++++B++++C++++D++++E---- > | | | > | | | > Well I suppose those short-circuit lines are related to avoiding turn time penalties, or artificially set them. This is in my part (well said it often enough) - the most important thing for good routing, the only workaround being what I wrote down in the patch before - but of course this adds to map size much more than short-circuits would do. Are these arcs visible within gpsmapedit? I have not seen them (maybe did not look well enough). > The + signs show a single road that has nodes A-E. Nodes B, C and D > have other roads connected to them. A and E are connected to other ways > but they also have a short-circuit arc (SCA) between them. I have seen > short-circuit arcs span from one end of a road to the other and also > from an inner node (like B, C or D) to one of the ends. Note that the > short-circuit arcs don't span roads, they just connect nodes within > single roads. > > I have been planning to do some experiments to get to understand this > more but have not found the time to do so yet. > > Cheers, > > Mark > _______________________________________________ > mkgmap-dev mailing list > mkgmap-dev at lists.mkgmap.org.uk > http://www.mkgmap.org.uk/mailman/listinfo/mkgmap-dev >
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