The increasing demand for navigation aids and sophisticated control systems in modern cars has led to a growing number of GPS applications in the automobile industry. In addition to position and velocity, precise attitude measurements are needed for many emerging control applications in cars, such as lane-keeping and collision avoidance systems. GPS can also be used to measure the attitude of a vehicle, and this approach offers a significant advantage over other methods in the tradeoff of accuracy vs. cost. However, few commercial GPS products exist with the capability of measuring attitude, and those that are available perform poorly in most urban environments and are prohibitively expensive for use in consumer vehicles
