Update on TT Replanning behaviour

[TonyD]

I have just done another return trip to Thame from Leeds and I took the opportunity to do some experimenting with my replanning problem. 3 times on this trip I opted not to take the TT indicated route and saw the following behaviour. On each occasion there was an immediate replan which was not the fastest route, the extra times being 10 minutes, 20 minutes and 25 minutes. This time though, I looked at the actual suggested route and it was not as I originally thought, turning back to the junction I had just passed, but instead cutting diagonally across country to regain the original route a little further up track. However, in each case, within a minute or two it had done a proper fastest route calculation and then given me the correct answer which is to carry on along the motorway to the next of my 3 routes and then given me the identical ETA to what it was before I overshot the junction. Previously, I had said it took 5 minutes to do this, I think it's just that I hadn't looked at it for 5 minutes.
So, I agree, not a serious problem in practice, but nevertheless of some academic interest. For some reason TT does an immediate "quick and dirty" reroute, followed pretty soon by a proper one. It might do that because as an immediate response it is quicker to only consider part of the route, but if that's the case it's a pretty misleading red herring because in one of my examples it added 25 minutes. It might do it because it has a programmed bias to try and stick to the original route, but in that case why replan the second time. Of course it might just do it because of a bug in the TT software (my favoured option).
Incidentally there was no traffic indicated on any of these examples. I also, experimented with Mr T's suggestion of doing an advanced planning simulation from a point a few hundred yards past the junction and quite predictably it came up with the proper fastest route.
I don't wish to open another can of worms, I've just posted the facts as I saw them above. But I am curious as to any other explanations of this behaviour and promise I won't shoot anyone down in flames for a comment I think is illogical
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Tony
(TT940)

[MrT]

I am only making assumptions here based on what you have said rather than from a knowledge of TT's algorithms.

I understand that TT routes backwards from your destination to your start or current point in a number of internal waypoints. When you go off route it quickly tries to reroute you to the next waypoint on your original route.

Something then happens, a traffic update, a timed rethink, no junctions for the next minute so it has time to recalculate without having to give you necessary directions, I don't know what, but that then reconsiders your whole route and then comes up with the optimum route from where you then are.

I do not know if this is a fault or just the way it works, but it has not caused me any issues whilst navigating yet.
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Drivelux

[GerryC]

I can see the point of a "quick and dirty" replan so that the user at least has some route to follow even if it's not great as soon as possible. Doing a proper replan in the background could then make a better guess at an ETA and better routing. I guess it's to stop the driver panicking when there is no route shown.
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Gerry
TomTom730T
Cameralert for Android
Brodit ProClip mount

[TonyD]

What you have both said seems plausible, just a bit strange that it doesn't immediately do the proper replan immediately following the "quick and dirty" one. There's definitely a hiatus here while it (apparently) does nothing.
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Tony
(TT940)

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