Tomtom Nav3 routing questions

ravi · Regular Visitor Joined: Aug 24, 2004 Posts: 119

Does anyone know how TTN3 comes up with its choice for routes at all?
I ask because as a new user, I am testing TTN3 on routes that I know to see how it varies from my well known routes and most of the time it seems to be ok but every now and then it seems to go a bit nuts!
For example, I made a journey from my home to Cardiff (about 30 miles away and the journey there was fine and predictable. When I asked it to find a route back home however ( a couple of hours later), it suggested a route that was way off track and totally different from the outward journey that it had suggested.
On a journey with the kids to Longleat it took me the usual way from the M4 throught Bath and then onto the A36 down to Longleat - this was the journey that I'd taken for years and years. On the way back however, It took me through a shortcut through Bathampton and a small toll bridge that quite frankly, saved almost 20 mins and bypassed Bath entirely!! I was amazed and thought WOW!!. Whenever I've subsequently tried to plan the route from home to Longleat again, it's never, ever come up with this shortcut again!!

How does it decide? Is it random?

lbendlin · Posted: Tue Aug 24, 2004 2:14 pm Post subject:

calculation really is pretty simple. You have pieces of roads with certain properties (average speed, one lane/two lanes, number of turns etc. that can all be translated into penalties. The connection between A and B with the least penalties wins.

What you need to keep in mind is that you will only get identical results if your point A is always the same, and if your tuning parameters are always the same. Being a few metres down the road at your starting point may already make the difference between one route or the other.

We have seen some applications (not TomTom) that are already doing "least turn" routing - where the penalty for turns is increased). Now what we are waiting for is that traffic lights are included in the penalty calculation. so far none of the programs has that...
_________________
Lutz

Report Map Errors here:
TomTom/TeleAtlas NAVTEQ

paulMac · Occasional Visitor Joined: Aug 28, 2004 Posts: 1

Hi ravi,
I am a new TT3 user and I have found the same as you - namely that a return journey can be significantly different to the outward.

I wondered whether it remembered the time taken on the outward journey and perhaps considered this to be too slow for the return and therefore looked for an alternative.

I also thought about the "right turns" policy.

Perhaps it just wants to give you a bit of variety!

lbendlin · Posted: Wed Sep 01, 2004 3:40 am Post subject:

Flat_Eric · Occasional Visitor Joined: Aug 18, 2004 Posts: 45

Is that true? Does it actually take into account right turns?
Mine nearly always calculates a slightly different return route unles I have the route algorithm set on STRICT, then it's far more accurate. I guess it also will depend on what you have set for your average speeds on the different classes of roads as to which route it thinks is faster, therefore preferable.

amcluesent · Posted: Wed Sep 01, 2004 11:38 pm Post subject:

I've no idea if TomTom use this particular route planning approach, but its a good description of one of the best shortest path algorithms - http://www.policyalmanac.org/games/aStarTutorial.htm

	PocketGPS
	Web