Tunnels.

gcb · Regular Visitor Joined: Oct 24, 2005 Posts: 151

What does your I3 do when you drive through a tunnel?

Please take tunnel to mean long tunnels over 150 metres,

I would have imagined when I drove though a tunnel that my I3 would complane about losing satalite connectivity. Doesnt seem to do this.

I only have experience of one such tunnel but:

When I drive through the tunnel, the I3 seems to show me driving through almost as if I were still in satalite reception.

When my destination is somewhere above and to the side of the tunnel, the I3 gets confused, moves me impossibly from in the tunnel to one of the roads above the tunnel and Hey presto , Destination on Left, Bing Bong, it thinks I arrived before I even get out the tunnel.

This kind of anomoly could easily be fixed in the software, if all tunnels were maked in the map data. So if unit suddenly lost reception at either end of a tunnel (maked in map data) it could know exactly where it was likely to be when it regained satalite reception.

zogman · Posted: Fri Nov 18, 2005 2:01 pm Post subject:

gps's know when theres a tunnel and compensate by estimating the distance and time taken to travel through it.....obviously if you stop in the tunnel then the gps will loose the signal after a set period ...
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gcb · Regular Visitor Joined: Oct 24, 2005 Posts: 151

I thought that should be the case , doesnt explain why my I3 was insisting that I turn left to destination half way through one.

Mr_Gonzales · Posted: Fri Nov 18, 2005 3:42 pm Post subject:

Mine gets me through the Medway tunnel (100-200m) but loses reception and takes a few seconds to get it back when going through the Dartford tunnel (half a mile?).

Having the display show the car/bike going through the water is always good for a laugh.

zogman · Posted: Fri Nov 18, 2005 3:46 pm Post subject:

Skippy · Posted: Fri Nov 18, 2005 5:58 pm Post subject:

Skippy · Posted: Fri Nov 18, 2005 6:01 pm Post subject:

Oh yeah, I forgot to add that the expensive ££££ in-car systems (and some top end Garmin models) have "dead reckoning" which monitors the wheel speed of your car and uses a gyroscope to determine your direction so it can compensate for a loss of signal from the GPS receiver...

zogman · Posted: Fri Nov 18, 2005 6:03 pm Post subject:

very informative explanation skippy...
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Mr_Gonzales · Posted: Fri Nov 18, 2005 11:54 pm Post subject:

That could explain why sometimes when I'm looking at the GPS it shows me on a nearby parallel road for a second, or why sometimes the i3 shows me taking a motorway turnoff/staying on the motorway when I'm doing the other of the two.

This only happens when I'm not navigating - when I'm just using it as a moving map. I guess when navigating it assumes you'll take the given route and after a few seconds before it realises you're going another way and it recalculates.

It definitely sounds like it's all down to the accuracy of the GPS and it getting confused when two roads are close by.

gcb · Regular Visitor Joined: Oct 24, 2005 Posts: 151

CF10 4JY.

This postcode is less than 100 ft from a tunnel (above the middle). The Building Future Inns , Cardiff Bay is closer to the tunnel than the road , this Probably confused the I3 which took the Tunnel to be like any other road which could have houses along the side of it. I would think this would catch out any GPS unless the GPS actually distinguished tunnels as tunnels.

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