Using land-vehicle steering constraint to improve the heading estimation of mems GPS/ins georeferencing systems

The integrated navigation systems of Global Positioning Systems (GPS) and Inertial Navigation Systems (INS) are used to provide direct-georeferencing for Mobile Mapping Systems (MMS). MEMS (Micro Electro-Mechanical Systems) inertial sensors have been developed to the stage that the GPS/INS integration systems based on low-cost MEMS IMU (Inertial Measurement Unit) are considered to be used as a cheap direct-georeferencing for mobile mapping, especially for the close-range vehicular photogrammetry systems. However, the limited performance of the MEMS sensors, especially the instability of the MEMS gyros, will give degraded orientation (e.g. heading) information, especially when the vehicle stops or creeps in traffic jams. This paper presents a method to mitigate such heading degradation under zero or low speed challenging conditions by using the steering constraint of the land vehicle, which stands for the fact that most of the land vehicles will have bounded turning rate under certain speed because of their minimum steering radii. When the speed is low or zero, the steering constraint becomes tight and therefore can suppress the heading drift of the MEMS GPS/INS. Real field test results are given in the paper to show the contribution of the steering constraint to the heading accuracy, using some typical low-speed and static cases as detail examples. With appropriate parameter adjustment and quality control mechanism of the steering constraint, the results show clear improvement to the heading estimation for zero/low speed scenarios; and have no major side-effect to the other scenarios, e.g. high speed case and real vehicles turns. The steering constraint is an effective method to mitigate the heading degradation in zero/low speed condition for the MEMS GPS/INS georeferencing systems.