Nonlinear Initial Alignment based on Quaternion Error Model

A quaternion based nonlinear model is designed for the Strapdown Inertial Navigation System (SINS) initial alignment with large initial errors. Furthermore, a filtering algorithm that can circumvent the norm constraint of the quaternion is developed to solve the quaternion based initial alignment problem. The simulation results indicate that the quaternion based initial alignment outperforms the Euler angle based method in terms of both alignment speed and accuracy. In this respect, the quaternion is more suitable for initial alignment with large misalignment angles.