[mkgmap-dev] Maps not for Cars and sharp-turns, U-Turns

Thu May 28 22:17:15 BST 2009

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.