[mkgmap-dev] Unusual Routing Behaviour in BaseCamp

Sat Nov 14 11:03:20 GMT 2020

Hi Dave

There are a few things going on here that might have effects on the
routing behaviours you are seeing.

Driving side - as Gerd has elaborated. I have an example where the
Garmin routing algorithm will do 2 left turns, a u-turn and then a
right turn anyway across the traffic to avoid the correct, single,
right turn!

I notice that Zambia has adjacent countries with drive-on-right, so you
need to beware of tiles around the edge of your map where the automatic
choice could be wrong for Zambia.

The default style uses type 0x08 and 0x09 for link roads and these are
thought to have special properties regarding pop-up hints, but not
known to effect routing decisions.

Link roads have the same road_class as their non-link equivalents so
this shouldn't have drastic effect on routing, but they do have a lower
speed, which should have favored the direct turn even more (being
shorter as well).

Changing between primary and secondary might have a small effect on
which roads get their angle into/out-of the junction adjusted where
they are at a tight angle (<= 45 degrees) from another road and the
turn appear permissible for navigation - tight angles impose a routing
penalty.

Ticker