“…To meet the requirements of accurate indoor heading estimation using a low-cost MEMS strapdown inertial navigation system, an effective method of quaternion-based UKF algorithm has been proposed. The quaternion-based UKF algorithm has the following advantages over the general Kalman filter and EKF [ 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 , 42 , 43 , 44 , 45 , 46 ]: (1) The quaternion-based orientation of an object has no singularities when the pitch angle passes through ± π /2 than Euler angles or Direction Cosine Matrix (DCM); (2) Quaternion-based matrix transformation has higher computational efficiency than Euler angles and DCM, and it is more suitable for our low cost MEMS multi-sensor system; (3) EKF models are linearized through a first order Taylor series expansion of the process/measurement models around the current state estimate, meanwhile, Jacobian matrix computation is quite complex; but UKF is second order approximation, which has capability of dealing with large and small attitude errors.…”