An attitude updating algorithm using Picard iteration and higher degree polynomial.

To accurately track body attitude under high dynamic environments, a new attitude updating algorithm for the strapdown inertial navigation system is proposed after further applying higher degree polynomial to the quaternion Picard iteration (QPI) algorithm. With QPI, calculation error introduced by Picard approximation can be eliminated, but the angular rate fitting error introduced by substituting polynomial for angular rate of body will still affect the accuracy of the attitude updating algorithms which are designed based on polynomial model. Hence, a five- rather three-degree polynomial constructing method using four samples of gyro outputs with coning motion constrain is designed and tested. Simulation results indicate the proposed method owns more accuracy than QPI, optimal coning algorithm, and Fourth4Rot under both low and high dynamic environments. [ABSTRACT FROM AUTHOR]