Describes a real time, on-the-fly, roll and pitch alignment algorithm for inertial measurement units (IMUs) mounted on land vehicles. Unlike conventional strategies, the alignment is achieved without external observations. This is achieved by exploiting the nonholonomic constraints that govern the motion of a vehicle on a surface to obtain the roll and pitch of the IMU. The position of the vehicle along its path is still unobservable and the algorithm is effective only when there is sufficient excitation in all degrees of freedom. However, with the proposed alignment algorithm, the IMU is able to provide sufficiently accurate position information for substantially longer periods of time compared with conventional methods. Experimental results are provided along with a comparison of an IMU/GPS navigation loop showing the effectiveness of the algorithm.
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