Identification of geometric displacements of odometers in a GNSS/inertial navigation system installed on a land vehicle

Abstract

An identification of geometric displacements of an odometer is a real-time determination of the odometer's lever arm vector relative to an IMU, determination of the IMUs frame attitude relative to a vehicle's body frame, and a refinement of an odometer's scale factor. Odometers measurements models for steering front wheels and for uncontrolled rear wheels have been developed in detail. Observability conditions of the geometric displacements on trajectories specific for a land vehicle have been considered. It is shown that by setting the odometer's lever arm components relative to the vehicle body, the observability of all three IMU's attitude angles on trajectories of a certain shape may be achieved. The partial observability of the geometric displacements in the absence of information about a steering angle of the front wheels has been described. Secondary observable combinations of the geometric displacements have been identified. Odometers measurement models have been reformulated in terms of these combinations. An iterative least-squares procedure has been developed for evaluation of these observable combinations in real time. Observation equations have been obtained for incorporating the odometer's measurements into an observation vector of a navigation loose-coupling Extended Kalman Filter. Experimental results obtained with the odometer, attached on both the front and rear wheels have been presented.