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[mkgmap-dev] Bicycle routing improvements (reverting breakage from r1431)

From Harri Suomalainen harri.suomalainen at iki.fi on Tue Aug 10 22:42:28 BST 2010

On 08/10/2010 11:32 PM, Marko Mäkelä wrote:
> kilometers of the route. In the middle of the route (after riding a
> couple of kilometers), it will instruct me to turn from the cycleway to
> the car road and continue on that. If the car road is tagged bicycle=no,
> it will instruct me to take a detour. For example, the 2*70 km route
> that I made last weekend would have been something like 280 km with the
> bicycle routing option, using lesser car roads. With car routing

I did some testing recently using Oregon 550 and Nuvi 755. My 
impressions were as follows.

It seemed that Garmin uses first road_class to select larger roads. That 
helps in making the road network reasonable in size I guess. If the 
larger roads are not connected, it uses smaller roads to get from a 
larger road to another. Same applies for the start and endpoint where 
you usually have to use small roads.

If you set a via point, it uses smaller roads to get into it as well 
(after getting nearby using the larger roads). (You can guide the 
autorouting quite a lot with those).

After it has selected the road network it starts computing the route 
such as faster or shorter. Shorter will yet prefer large roads becacuse 
the network consists mostly of them (or the smaller roads are ignored on 
a long route).

I got very good bicycle routing when I used road_class=4 or 3 for 
paved/unpaved cycleways. It always preferred the cycleway instead of the 
parallel car road (which was lower in road_class).

Unfortunately that had a major impact. By raising all the cycleways to 
high road_class the computation time for the route was very 
unacceptable. Route calculation (and recalculation!) time for a 20km 
test route in Helsinki was about 2-3 minutes with Oregon.

The end result was that raising the road_class is the major parameter 
and speed being far behind that.

My impression was that the route length matters a lot too. Longer route 
would have a huge network of small roads ie. Garmin starts ignoring 
them. For a short route that is not an issue.

>> Only road_speed=0 and road_speed=1 are taken for route priority,

I'm interested in that one too! (even if my results were that speed is 
not that important. However, I had speeds 0-2

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