Made some test. during fastest route serching, garmin gives a time penalty to turns. time penalty seems propotional to road speed so I think it just calculates a speed reduction due to turn and then a linear increase of speed up to the road speed. for a steep 15° turn I got 357 second penalty on a motorway (road_speed=6 i.e 108km/h) and 237 second penalty on a primary (road_speed=4 i.e. 72km/h) as the angle widens, the penalty is reduced (at 45° is about 1/3 the above values, at 90° about 1/8) Ciao, Marco. --- Gio 28/5/09, Felix Hartmann <extremecarver@googlemail.com> ha scritto:
Da: Felix Hartmann <extremecarver@googlemail.com> Oggetto: [mkgmap-dev] Maps not for Cars and sharp-turns, U-Turns A: "Development list for mkgmap" <mkgmap-dev@lists.mkgmap.org.uk> Data: Giovedì 28 maggio 2009, 23:17 After playing around a bit with maps and getting really confused why on some ways I could not route along with car/motorcycle setting, even though all access restrictions were sorted out, I found out that in case of very low angle of roads meeting, in car/motorcycle setting huge detours maybe made just to turn around.
This is quite impractical as the best routing performance can be achieved with the car/motorcycle setting when writing the maps in such a way that bicycle use is assumed to be used as car/motorcycle. Using a bicycle there is no need to prohibit any kind of u-turn, but I think we can't get this out of the garmin programming but by changing the data source. Has anyone any idea how we could sort out this problem with preprocessing?
Actually this might be usefull for car/motorcycle uses as well. It would be better to rely on turn-restrictions than on the garmin GPS simply deciding that at some place turning is impossible and making a detour to turn! I don't know the angle but I think if the meeting angle is lower than somewhere around 20° this happens. So roads meeting would need to be changed to meet at bigger angles than 20°. To really find out the angle upon which Garmin GPS/Mapsource decide a car can't turn (note avoid U-turn is not activated of course) would need some test maps however.
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