Yes, Osmo wrote an absolutely brilliant application and its a joy to work on it.

As for what to do when GPS is lost: for my liking, its too many unknowns to predict position reasonably. It would matter only in the tunnels with the branches, but then we don't know which one you took. Don't forget, its frequent when we reduce speed in the tunnel as well. From GPS POV, you will loose the signal that will have to be restored - so after tunel we will have a short break as well.

The alternative would be to switch to car's speedometer, compass, and from these try to predict the motion. I think that could come one day to Qt, if it hasn't done yet, but for the car industry mainly.

So, unfortunately, its a bit too far at foreseeable future.