How does Sat/Nav work in tunnels???

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01-09-2008, 11:27 AM

#11

ImolaRedM

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Quote:

Originally Posted by Rudy' post='515115' date='Jan 8 2008, 12:36 PM

Exactly. As a matter of fact, the earliest integrated nav systems from manufacturers like BMW and M-B used dead-reckoning in addition to the signal from the satellites to keep things as accurately as possible. Keep in mind that in these earlier days, there was a built-in error from the signal sent by the GPS satellites for consumer (non-military) applications -- called Selective Availability, or "SA". SA added an error to the signal that amounted to about 10 meters (32 feet) so the cars were constantly updating their positions based on the data received from the satellites as well as the dead-reckoning sensors on the car.

SA is currently disabled and has been since some time in 2000 and is not likely to ever be enabled again...

Yup, I remember when SA was still active I had accuracy to within a few feet in my E39. I also recall that the system would re-calibrate when you made 4 right hand turns (around a block). A friend of mine was showing off his new Acura and his Nav placed him across the street and down the road while my E39 had us correctly placed in the parking lot at work.

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01-09-2008, 11:34 AM

#12

kchan

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My Ride: 07 BMW 525i Premium Package, Xenon Lighting Package, manual Transmission. Titanium Grey, 20% Tint around the back, 70% V-Kool on front. Planned mods: Style 71 wheels with Toyo Proxy 4 tires, Sachs suspension upgrade, upgraded stereo, and many more to come.

Quote:

Originally Posted by swajames' post='515593' date='Jan 9 2008, 12:25 PM

that's right, I have a 920T in my Honda Pilot, it's excellent.

I have the 920 (without the T) and I like it alot too! How's the traffic info works out in the bay area? I think the voice recognition works pretty well too, what a bargain from costco.

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01-09-2008, 01:01 PM

#13

swajames

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My Ride: 2008 Porsche 911 Carrera S Convertible. Midnight Blue, 6 Speed.Retired - 2007 997 Carrera S, Midnight Blue, Grey leather, premium audioRetired - 2007 550i, Monaco Blue over Beige, Navigation, Logic 7, Cold Weather Pack, Comfort Access, Sport Package

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Quote:

Originally Posted by kchan' post='515602' date='Jan 9 2008, 12:34 PM

I have the 920 (without the T) and I like it alot too! How's the traffic info works out in the bay area? I think the voice recognition works pretty well too, what a bargain from costco.

I've not used it too much to be honest but it does work pretty well (I'm normally on 85/280 and it does seem to pick up quite a lot of traffic info). Only downside is you have the receiver trailing out the bottom of the unit but other than that it's pretty good. It will reroute too but I never use that as I'm typically caught on the freeways no matter what!