Navigation in a tunnel: the guidance keeps running without GPS
In a tunnel the phone reports no usable GPS, and a navigation freezes or jumps. DriveBattle for Android carries the position forward along the route, keeps announcing and blends to the real fix after the tunnel. The recorded ride then has no gap.
What happens after four seconds
If no GPS fix arrives for four seconds, the cockpit shows the notice “GPS signal lost - position estimated”. From then on the app advances position, progress on the route and spoken announcements every 500 milliseconds along the route geometry. The basis is the last credible speed. If the vehicle is below 3 km/h, the estimated position stops.
Known tunnels may run longer
When it calculates the route, the server also asks the road network which sections are tunnels. In a known tunnel the advance runs for up to 20 minutes, because the tube has no junction where a guess could go wrong. Outside a known tunnel the position freezes after 2 minutes, so that it does not run on forever if you are actually stuck in a jam or have turned off. The offline router delivers no tunnel marking, so the 2-minute limit always applies there.
The receiver counts along
The app also watches the GNSS receiver. If it sees no satellite for at least 3 seconds, this counts as a tunnel, even if the route knows no tunnel. The app then checks every fix more strictly. In this case the advance itself runs only up to the normal limit of 2 minutes, the 20 minutes apply only in a tunnel that the route calculation knows.
False positions are discarded
In a tunnel the phone often delivers positions from cell towers and Wi-Fi, with errors of hundreds of meters. The app discards such fixes. A fix must be accurate to 50 meters, in a tunnel to 20 meters, and it must not jump at more than 300 km/h away from the last assumed fix. A discarded fix does not count as a sign of life, otherwise it would end the advance. After a gap the app accepts reception again only after two fixes that match each other.
After the tunnel
When a real fix arrives again, the display blends to it within 1.5 seconds instead of visibly jumping. This applies to small offsets. A large offset means the estimate was wrong, for example because you stood in a jam inside the tunnel. In that case the display jumps honestly to the real position.
The ride has no gap
The recording benefits too. On upload the server closes gaps of at least 8 seconds and 150 meters over the road network, before elevation profile and statistics are calculated. It spreads the timestamps evenly over the gap. It accepts a replacement piece only if it fits the measured time (3 to 200 km/h) and is not longer than 2.5 times the straight-line distance. Otherwise it stays a gap, for example at a stop at a petrol station with poor reception. Per ride it fills at most 20 gaps, and a single gap may be at most 30 minutes and 30 kilometers long. The kilometers in the tunnel count toward the distance.
In the car
With Android Auto the turn notice shows “GPS lost” as long as there is no signal, instead of outdated distances. Android Auto is Premium.
What the estimate cannot do
The position in the tunnel is an estimate from the last speed. If you stand in a jam, it keeps running until the tunnel ends or the limit is reached. The app does not state an accuracy in meters. The tunnel improvements are available from version 0.22.36. Older versions advance the position for at most 2 minutes. The feature is free.
Frequently asked questions
- Does navigation work in a tunnel without GPS?
- Yes. After four seconds without a fix the app shows “GPS signal lost” and advances position and announcements along the route.
- How long does the navigation keep running in a tunnel?
- In a tunnel that the route calculation knows, up to 20 minutes. Otherwise the position freezes after 2 minutes.
- Does the position jump after the tunnel?
- With a small offset the display blends to the real fix within 1.5 seconds. With a large offset it jumps to the real position.
- Does my recorded ride have a gap in the tunnel?
- As a rule, no. The server fills gaps of 8 seconds and 150 meters or more over the road network, if the piece fits the measured time.
- Does this also work offline?
- The advance does. The offline router knows no tunnels, though, so the limit of 2 minutes applies there.
- Is tunnel navigation Premium?
- No. Only Android Auto as a whole is Premium.