Sat-nav still works in tunnels ... how?

threethirty · 01-16-2008, 10:41 AM

The BMW sat-nav continues to work even when there is no clear view of the sky, eg in tunnels and multi-storey car parks.

How?

I have a handheld GPS which fails immediately under trees, even heavy cloud. But the BMW system works all the time.

I have a theory that actually, satellite reception IS lost in tunnels, but the mapping software combined with the speed and direction of the travel is enough to keep the system running.

E92Fan · 01-16-2008, 10:58 AM

The BMW satnav also uses the ABS sensors on each wheel to determine the rotational speed, and therefore the distance travelled. That's why even in a tunnel the satnav keeps track of where you are...

NFS · 01-16-2008, 11:09 AM

Quote:

Originally Posted by E92Fan

The BMW satnav also uses the ABS sensors on each wheel to determine the rotational speed, and therefore the distance travelled. That's why even in a tunnel the satnav keeps track of where you are...

That is why it's worth £1900

When I had TomTom the signal used to drop every time I was in London because I lost the line of sight to the satellite.

NathanJT · 01-16-2008, 11:42 AM

Tomtoms also TRY to use dead reckoning as they have (or at least had) an accelerometer in them. It just doesn't work anything like a well as the integrated system in the BMW.

booforty · 01-16-2008, 11:53 AM

Now that is interesting. You learn something new everyday...

CrimsonRedE93 · 01-16-2008, 12:22 PM

+1 a wealth of useful information

ShereKhan · 01-16-2008, 12:30 PM

Quote:

Originally Posted by NathanJT

Tomtoms also TRY to use dead reckoning as they have (or at least had) an accelerometer in them. It just doesn't work anything like a well as the integrated system in the BMW.

It only works well if you apply the quickfixes released every two weeks.
Otherwise it can be quite sluggish.

Del · 01-16-2008, 12:41 PM

I've noticed this with my Tomtom. It can't be that hard to predict where you are in a long tunnel. If you enter the Dartford tunnel at 60mph, the SatNav should assume you're still doing 60mph. Chances are you're not going to be turning left or right or stopping in the tunnel.

SoYank · 01-16-2008, 12:56 PM

Quote:

Originally Posted by Del

I've noticed this with my Tomtom. It can't be that hard to predict where you are in a long tunnel. If you enter the Dartford tunnel at 60mph, the SatNav should assume you're still doing 60mph. Chances are you're not going to be turning left or right or stopping in the tunnel.

Wanna bet?

mjh93sa · 01-16-2008, 01:50 PM

There are two types of dead-reckoning used in portable units (as I understand). If you spend enough money they'll put in some accelerometers, otherwise they'll just assume you keep moving (so an average or last known speed) along the route indicated.

beemerbird · 01-16-2008, 02:44 PM

That's interesting then, I wondered how come it still worked whilst driving through the Tyne tunnel a few weeks ago.

jwbmw · 01-16-2008, 02:53 PM

Quote:

Originally Posted by beemerbird

That's interesting then, I wondered how come it still worked whilst driving through the Tyne tunnel a few weeks ago.

I take it that you are talking about the Nav system Helen and not any other type of electrical toy?

beemerbird · 01-16-2008, 02:58 PM

Quote:

Originally Posted by jwbmw

I take it that you are talking about the Nav system Helen and not any other type of electrical toy?

Definately the sat. nav. Jason, don't like any distractions whilst driving

jwbmw · 01-16-2008, 02:59 PM

Quote:

Originally Posted by beemerbird

Definately the sat. nav. Jason, don't like any distractions whilst driving

Glad you keep your mind on the job in hand

01-16-2008, 10:41 AM	#1
threethirty Second Lieutenant 14 Rep 204 Posts Drives: BMW 330i M Sport Saloon 2006 Join Date: Sep 2007 Location: East Sussex, UK iTrader: (0)	Sat-nav still works in tunnels ... how? The BMW sat-nav continues to work even when there is no clear view of the sky, eg in tunnels and multi-storey car parks. How? I have a handheld GPS which fails immediately under trees, even heavy cloud. But the BMW system works all the time. I have a theory that actually, satellite reception IS lost in tunnels, but the mapping software combined with the speed and direction of the travel is enough to keep the system running. __________________ BMW 330i M Sport Saloon - 06 plate - Le Mans Blue
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01-16-2008, 10:58 AM	#2
E92Fan Moderator 322 Rep 5,493 Posts Drives: . Join Date: Aug 2007 Location: . iTrader: (0)	The BMW satnav also uses the ABS sensors on each wheel to determine the rotational speed, and therefore the distance travelled. That's why even in a tunnel the satnav keeps track of where you are... __________________ ... ... ... DMS Remap Review ----- Quaife LSD Review ----- Hartge Antiroll Bars Review ----- Bilstein PSS10 B16 Ride Control Review ----- Detail by ShineOn ----- Paintshield Review
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01-16-2008, 11:42 AM	#4
NathanJT Techie Geek 37 Rep 681 Posts Drives: 330d M Sport Manual Join Date: Jan 2007 Location: Derby, UK iTrader: (0)	Tomtoms also TRY to use dead reckoning as they have (or at least had) an accelerometer in them. It just doesn't work anything like a well as the integrated system in the BMW. __________________ 330d M-Sport \| Sapphire Black \| Black Dakota \| Nav Pro \| iDrive \| Bluetooth \| PDC \| Xenons \| Hot Seats \| Tracker \| Blacklines
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01-16-2008, 11:53 AM	#5
booforty Major General 337 Rep 8,811 Posts Drives: E92 M3 Join Date: Mar 2005 Location: London, UK iTrader: (0) Garage List 2008 E92 M3 [0.00]	Now that is interesting. You learn something new everyday...
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01-16-2008, 12:22 PM	#6
CrimsonRedE93 Major 108 Rep 1,085 Posts Drives: Le Mans Blue E93 330d+ Join Date: Nov 2007 Location: West Sussex iTrader: (0) Garage List 2007 E93 320I SE [0.00]	+1 a wealth of useful information
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01-16-2008, 12:41 PM	#8
Del New Member 2 Rep 16 Posts Drives: BMW e90 330i M Sport Join Date: Jan 2008 Location: South iTrader: (0)	I've noticed this with my Tomtom. It can't be that hard to predict where you are in a long tunnel. If you enter the Dartford tunnel at 60mph, the SatNav should assume you're still doing 60mph. Chances are you're not going to be turning left or right or stopping in the tunnel.
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01-16-2008, 01:50 PM	#10
mjh93sa Major General 147 Rep 5,080 Posts Drives: 530d Join Date: Dec 2005 Location: Gloucestershire iTrader: (0) Garage List 2012 BMW M135i [10.00] 2011 Mini Countryma ... [5.50]	There are two types of dead-reckoning used in portable units (as I understand). If you spend enough money they'll put in some accelerometers, otherwise they'll just assume you keep moving (so an average or last known speed) along the route indicated. __________________ Gone: Fiesta - Focus - E46 320dSE - E91 330dMSport - E82 135iMSport - R55 JCW Clubman - M135i Now: 530d
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01-16-2008, 02:44 PM	#11
beemerbird Major General 172 Rep 7,953 Posts Drives: Merc diesel Join Date: Oct 2007 Location: Yorkshire iTrader: (0) Garage List 2010 TTRS [9.00] 2007 Audi S5 [0.00] May 2007 Porsche 99 ... [0.00] March 2007 Porsche ... [0.00] Sep. 2007 E92 335d SE [0.00] July 2006 E90 330i ... [0.00]	That's interesting then, I wondered how come it still worked whilst driving through the Tyne tunnel a few weeks ago.
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