[mkgmap-dev] Commit: r1410: Add --merge-lines option to combine lines at lower zoom levels.From Mark Burton markb at ordern.com on Tue Dec 1 21:43:25 GMT 2009
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---- | | | | | | 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
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