The difference between the left and right invariant extended Kalman filter

• Left and right IEKFs are identical when a proper reset step is used. • Discretising the continuous-time filter ODEs yields difference between left and right IEKFs. • Same equivalence holds for discrete-time systems as well. • Global navigation example shows including reset improves asymptotic performance. The extended Kalman filter (EKF) has been the industry standard for state estimation problems over the past sixty years. The invariant extended Kalman filter (IEKF) [Barrau and Bonnabel, 2017] is a recent development of the EKF for the class of group-affine systems on Lie groups that has shown superior performance for inertial navigation problems. The IEKF comes in two versions, left- and right- handed respectively, and there is a perception in the robotics community that these filters are different and one should choose the handedness of the IEKF to match handedness of the measurement model for a given filtering problem. In this paper, we revisit these algorithms and demonstrate that the left- and right- IEKF algorithms (with reset step) are identical, that is, the choice of the handedness does not affect the IEKF’s performance when the reset step is properly implemented. The reset step was not originally proposed as part of the IEKF, however, we provide simulations to show that the reset step improves asymptotic performance of all versions of the filter, and should be included in all high performance algorithms. The GNSS-aided inertial navigation system (INS) is used as a motivating example to demonstrate the equivalence of the two filters.