Online IMU Intrinsic Calibration: Is It Necessary?

Abstract

This paper addresses the problem of visual-inertial self-calibration while focusing on the necessity of online IMU intrinsic calibration. To this end, we perform observability analysis for visual-inertial navigation systems (VINS) with four different inertial model variants containing intrinsic parameters that encompass one commonly used IMU model for low-cost inertial sensors. The analysis theoretically confirms what is intuitively believed in the literature, that is, the IMU intrinsics are observable given fully-excited 6-axis motion. Moreover, we, for the first time, identify 6 primitive degenerate motions for IMU intrinsic calibration. Each degenerate motion profile will cause a set of intrinsic parameters to be unobservable and any combination of these degenerate motions are still degenerate. This result holds for all four inertial model variants and has significant implications on the necessity to perform online IMU intrinsic calibration in many robotic applications. Extensive simulations and real-world experiments are performed to validate both our observability analysis and degenerate motion analysis.