A Coarse Alignment Method Based on Digital Filters and Reconstructed Observation Vectors.In this paper, a coarse alignment method based on apparent gravitational motion is proposed. 
Digital Filters
To extract the effective observation vectors from the inertial sensors' outputs, a parameter recognition and vector reconstruction method are designed, where an adaptive Kalman filter is employed to estimate the unknown parameters. 
Kalman filter
Furthermore, a robust filter, which is based on Huber's M-estimation theory, is developed for addressing the outliers of the measurement observation vectors due to the maneuver of the vehicle. 
Huber's M-estimation theory