Route Calculation

R1chard · Regular Visitor Joined: Feb 07, 2004 Posts: 64

I make regular trips between my home in Cheshire and Newcastle, a distance of about 200 miles. Although I know the way I usually have TTN running with Checkpoint so I'm reminded about speed cameras. Going to Newcastle (usually starting before 5.00 am when the roads are clear) I follow the route as calculated by TT2 which involves M60, M62, M1, A1(M) but when I return (usually during the early evening) I choose to ignore TT2 and go over to Carlisle and down the M6. I know this route is about 10 miles longer but is likely to be quicker at the time of day I use it because the M62 around Manchester can be a nightmare during the rush hour. (Still with me?)

Today, when leaving Newcastle, TT2 decided for the first time to route me along my chosen route (the M6) rather than its normal route (the M1). It's almost as if it has some intelligence which says "If he always ignores the route I choose then I'll choose the route he always takes". Of course I know that's not happening but what is going on here? Why should TT2 suddenly decide after many weeks to choose a new route when everything else remains equal?

Richard

lbendlin · Posted: Thu Mar 04, 2004 1:55 am Post subject:

You may have initiated route calculation in an area where both routes are appealing in pretty much the same way, and it may be a matter of a few yards if the libra leans to one or the other option. Or you may have played around with road speeds...

Eventually there's no magic involved in the calculation. You have a set of road segments with their respective speeds, and you have a set of restrictions/penalties (like "right turns are bad and get a penalty of one minute") . Then all the app needs to do is walk the mesh and find the path with the smallest penalty. Ok, so there's a little bit of magic every here and there... but not much ;-)
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bigfatjohn · Posted: Thu Mar 04, 2004 12:23 pm Post subject:

From my house, to go east, there are two more or less equal routes to reach the A14 at Thrapston, about fiteen miles away.

What I find funny is that when going away TomTom consistently picks one route but when coming home it unfailingly chooses the other.

lbendlin · Posted: Thu Mar 04, 2004 3:02 pm Post subject:

As I wrote before, the return route will most definitely have different penalties. A left turn on the original route will be a right turn on the route back, and this will get a higher penalty.
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