Aid2GPS is a failsafe system for localization of a vehicle, even at times when GPS is unavailable. It employs an optical flow sensing based odometry system and a digital compass to track position and orientation.
WORKING (in a nutshell): Initially a GPS reading is taken to globally localize the vehicle. The backup system then kicks in. Later when the vehicle enters a GPS denied region, the previously measured GPS location coordinates and backup system data are fused together to effectively localize the vehicle. We thus have a never-be-lost system for automobiles.
The system is currently implemented on a mobile robot platform. I am currently working on its data fusion, and map display. The optical flow - digital compass system is complete and functional.