For critical functions - combination of inertial navigation systems, mapping, radar, and plain old visual recognition of the location - after all, you need to have a sophisticated visual recognition system anyways to scan for all of the dynamic activity, why not extend it to be more broadly used? GPS is okay for gross navigation and tracking, just don't design any critical life-safety system to rely on it. I'd be very surprised if there were any boats/cars/planes that absolutely required GPS to be functioning for safe operation beyond the higher level navigation functions. Very disappointed as well.