Issue with route given by GPS

[silverbeauty]

While I was in the tunnel I changed speed from 80km/h to 60km/h and the GPS changed speed to reflect my actual speed. Unless there is some sort of accelerometer in the GPS I can't really see how it would do that without some sort of external transmission. My GPS is a Garmin 1460.

GPS does not loose satellite signal immediately ... you can go quite a distance before it does ...

[DPBaker]

Yes, I go through the tunnel at The Curve a few times a week as well as the one near Genting, so am pretty used to how long the GPS goes before losing lock - usually just before the end of the tunnel. But one tunnel I was driving through in Singapore is at least 5 times as long and it didn't lose lock at all. Also the speed changes wouldn't occur if it was just dead reckoning.

[gpsnerd]

maybe its better to view the route rundown before u proceed to make sure u are guided on the right track

[vash_h]

if not mistaken, i read somewhere that singapore installed repeaters in their tunnels so you can continue to use ur gps navigation, cell phones in tunnels..

[DPBaker]

if not mistaken, i read somewhere that singapore installed repeaters in their tunnels so you can continue to use ur gps navigation, cell phones in tunnels..

I suspect that too, but can't figure out how that would work - if you had a fixed antenna outside the tunnel then just re-radiated it, all the gps units inside the tunnel would show the position of the receiving antenna outside the tunnel. It must be a more technical setup than just re-radiating. I am just inquisitive and like to know how things work! :-)

[EastMushu]

Cell phone repeater yes but doubt so for gps though as have travelled KPE a few times and signal will be lost before the car exits the tunnel...

[Redstorm]

Cell phone repeater yes but doubt so for gps though as have travelled KPE a few times and signal will be lost before the car exits the tunnel...

It is not any kind of repeaters used inside our outside the tunnels. Only when using either Garmin CN or MSM maps, the device will go into simulation mode once it lose signal inside the tunnel, provided the vehicle travels at a constant speed from the time it enters and exit the tunnel. Fluctuation in speed inside the tunnel should not be a lot otherwise the simulation mode will not work. What they actually did is some coding on the maps to get the simulation to work when it loses signal.

[DPBaker]

That may be true except that:

- the gps changed speed when I changed speed - I deliberately went from 80 down to 60 and the gps changed accordingly - I went through these tunnels 4 times over a 2 day period so had plenty of testing time.

- I am very used to my own gps and I know how long before it looses lock in the Genting tunnel and the Curve tunnel - usually just before the end or just at the end. The tunnels in Singapore are maybe 5 times as long, yet it never lost lock once.

So, I can't really explain it. And to put it in context - I have been an Electronics Engineer for over 30 years and my company specialises in tracking equipment (for ships and helicopters) using GPS, so I work with GPS every day.

[Inggo]

Simulated Gps in tunnel working with Papago, but not more than 2 minutes.
There was gps repeater for L1/L2 RF signal in singapore tunnel.

[wblee]

I asked a fren in Singapore to test GPS in tunnel.
He tested tunnel at Kalleng-PayaLabar Expressway (KPE), and it fail with iphone GPS with papago. And giving woring location with iphone GPS + A-GPS with google maps.
it should be no GPS signal inside the tunnul.