Originally Posted by Aileron
Thanks for that referral. To add something here to one of the messages there, not all GPS units go kaput if they lose the signal. The built-in GPS in my Mercedes reverts to dead reckoning. It's interesting to see your progress through, for example, the Brooklyn Battery Tunnel when you are ten floors below sea level.
The new generation of SIRFStar receivers work indoors as well, that is the future of GPS, no longer requiring a clear sky will make for much better navigation.
Most GOOD car systems, like the one in your Mercedes don't use GPS as their primary navigation system, they use a tacho sensor and gyro's. The GPS is only used to determine the start and end point should it have lost that.