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DiscoDunc
Member Since: 08 May 2006
Location: Bristol
Posts: 16390
  
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| SatNav lost GPS but coords still being received. |
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I had a strange SatNav occurence today....
I was travelling down the M42 with my route home plotted when suddenly the GPS text appeared in the top left hand corner of the screen with a red line through it. The arrow on the screen then got completely lost and whilst still showing i was travelling, show me travelling at a totally wrong location. it was still showing a route and an arrival time though 
This continued for about 20 mins after which i cancelled the route guidance.
However, if I checked the off-road GPS the bearing, Northing and Westing and the compass seemed OK and the coords kept updating as expected.
after cancelling the route the lack of proper location continued. After about 15mins the GPS text in the top left hand corner suddenly disappeared and the location immedeatly plotted me in the correct place.
any ideas ? Duncan
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If I'd known I was going to be so thirsty this morning I'd have drunk more beer last night.
FFRR Autobiography 4.4 SDV8 MY17
D4 HSE MY13 SOLD
FFRR 3.6 Vogue TDV8 SOLD
D4 HSE MY10 SOLD
D4 SE TECH MY15 SOLD
D4 XS MY12 SOLD
D4 HSE MY10 SOLD
D3 HSE MY06 - Re-Cycled Worldwide
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 9th Jan 2009 8:24 pm |
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NJF
Member Since: 05 Oct 2007
Location: Gone
Posts: 2466
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Accelerometers built into the car permit it to continue tracking by dead reckoning when GPS signal is lost (which is why it tracks through tunnels)? The same accelerometers are used by the traction control system to determine when the car's speed, direction, yaw, tilt are outside safe limits?
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| 9th Jan 2009 8:33 pm |
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DiscoDunc
Member Since: 08 May 2006
Location: Bristol
Posts: 16390
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mmm, so any ideas why the sat signal was lost, for 35 mins. It also got my direction and bearing correct though, and i changed direction from West to South so it knew which direction i was travelling. is it that clever ? Duncan
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If I'd known I was going to be so thirsty this morning I'd have drunk more beer last night.
FFRR Autobiography 4.4 SDV8 MY17
D4 HSE MY13 SOLD
FFRR 3.6 Vogue TDV8 SOLD
D4 HSE MY10 SOLD
D4 SE TECH MY15 SOLD
D4 XS MY12 SOLD
D4 HSE MY10 SOLD
D3 HSE MY06 - Re-Cycled Worldwide
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| 9th Jan 2009 8:37 pm |
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NJF
Member Since: 05 Oct 2007
Location: Gone
Posts: 2466
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A pair of accelerometers used orthogonally can detect turns, which is why the car can navigate by dead reckoning for quite a while without verifying its position by GPS.
Reasons why you lose GPS might be (1) driving through a valley with insufficient number of satellites on the horizon to get a fix; (2) unlikely signal attenuation by exceptionally bad weather; (3) the Chunnel; (4) electromagnetic interference from an external or internal source; (5) Your car's GPS system is all stuffed up?
There is definitely a GPS dead spot near Saarbrucken, where we suffer from problem (4) above, with symptoms very like those you have described. It happens each time I drive there. It's near a (US Air Force, I think) signals station and at one point the autobahn is covered by an overhead wire mesh, which I guess is meant as some form of Faraday shield.
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| 9th Jan 2009 8:46 pm |
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DiscoDunc
Member Since: 08 May 2006
Location: Bristol
Posts: 16390
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gps must be knackered then
35mins without GPS at 80mph is a long way. its never happend before on the M42 and ive travelled that route many times.
best get it into the dealers then
thanks  Duncan
-----------------------------------------------------
If I'd known I was going to be so thirsty this morning I'd have drunk more beer last night.
FFRR Autobiography 4.4 SDV8 MY17
D4 HSE MY13 SOLD
FFRR 3.6 Vogue TDV8 SOLD
D4 HSE MY10 SOLD
D4 SE TECH MY15 SOLD
D4 XS MY12 SOLD
D4 HSE MY10 SOLD
D3 HSE MY06 - Re-Cycled Worldwide
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| 9th Jan 2009 10:29 pm |
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Popelka
Member Since: 31 May 2008
Location: Praha (Prague)
Posts: 2430
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cant add anything to this but want to say thanks for the explanation given by NJF, is this likely to happen for a portable unit like a TomTom I noticed going thru a tunnel it still tracked me even thought the signal had gone.
On another occasion I didnt get a signal until getting out of the city centre and away from the wires supporting the tram powerlines.
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| 10th Jan 2009 12:21 pm |
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