A GPS/Dead Reckoning System for Tracking and GIS Appliczhions

With the advent of worldwide 24 hour three- dimensional GPS coverage, the utilization of GPS by business has become routine. In vehicle tracking, GPS is now a reliable alternative to other technologies. In dense urban areas, however, GPS coverage will remain limited. To provide uninterrupted coverage of positional output even in urban areas, GPS can be augmented with a Dead Reckoning (DR) system. The GPS/DR system, developed by Trimble Navigation, adds a low-cost vibrational single axis gyro and odometer signal from the vehicle to a GPS receiver to maintain positioning capability even when GPS signals are being blocked by buildings or other obstructions. The system is able to maintain an accurate solution even after prolonged GPS outage by continuously calibrating the odometer, while GPS is available, and the gyro bias, whether or not GPS is available. The GPS/DR system can operate in a real-time tracking system mode or in a post-process capable GIS mode. In the tracking mode, a blended solution of GPS and DR data is output to the Automatic Vehicle Location (AVL) system. In the GIS mode, the GPS data is output directly, when available, and the DR solution propagates from the most recent GPS solution whenever GPS is unavailable. Each mode uses a Kalman-like heading fitter which maintains the heading accurately in both differential and autonomous GPS operation. In the system’s real- time tracking mode, the user has the added benefit of minimizing the errors due to reflected signals, another problem in the urban environment. Results are presented from differential and autonomous GPS/DR in the real-time blended mode.