A GNSS/INS-integrated system for an arbitrarily mounted land vehicle navigation device

For the traditional implementation of inertial navigation system, aligning the inertial sensor axes with the vehicle body frame is a necessary process. While the development of micro-electromechanical system brings considerable cost and size advantages, the undesirable alignment process is still a challenge for widespread civil use of portable inertial devices. Aimed to avoid complicated manual mounting of an inertial device used in land vehicle navigation systems, an algorithm is proposed to automatically estimate the misalignment angles between the sensor platform and the vehicle body frame, which enables the device to be mounted in an arbitrary orientation. The foundation of this method is formed by two facts. The first is that the accelerometer can exactly estimate its own posture when it is stationary on the platform. The second is the yaw calculated from the horizontally aligned device has a constant error when the horizontal component of the angular velocity is zero. A robust motion mode recognition technique, which compares the statistical characteristics of the measurements with an empirical threshold, is applied to detect whether the vehicle is parking, turning, or moving straight. Validation experiments show that the error of the coarse estimation algorithm is within 2° when the heading misalignment is less than 45°. This guarantees that the arbitrarily mounted device achieves the equivalent performance as the well-aligned one, whenever the global navigation satellite system (GNSS) signal is available. In addition, the positioning error of the misaligned device during short GNSS signal blockage is within 7 m with the application of auxiliary velocity updates.