[mkgmap-dev] More on Routing

Thu Jul 16 20:58:18 BST 2009

I've had a chance to play a little with routing today and noticed a
couple of things. An example would explain this best so here goes.

If routing from north of Manchester to somewhere along the M62 westbound
then the route is as expected (M66 onto M62 at J18, M60). Bury to Roe
Green is an example of this.
Bury to Gorse Covert however starts on the M66, turns off at J3, goes
through Whitefield and back on to the M60/62 at J17, travels past Roe
Green and arrives at destination.
Bury to CHester however starts along the M66, goes straight through
junction 18 to the next junction where you go all the way round the
roundabout, come back on yourself to junction 18 and then turn left onto
the M60 where the route is then as expected.This odd behaviour then
continues if routing to places further afield that require the same
initial route.

http://www.openstreetmap.org/?lat=53.5497&lon=-2.261&zoom=14&layers=B000FTF
shows the junctions involved but I can't see how it can be data errors
as some routes go M66, M62 westbound without problem and all 3
destinations mentioned above are on the same tile

Additionally I will occasionally get the odd routes previously described
when routing long distances but usually get the optimal route (this is
from the exact same starting point.

I realise there's a lot that's not yet fully understood in the img file
so I just thought I'd report these observations in the hope that they
can somehow add to the overall picture

Cheers

Paul

P.S. The routes described are as given by my Edge 605 and not simulated
through software