Authors: Bharat Joshi, Ioannis Rekleitis
Abstract: This paper presents an extension to the Visual Inertial Odometry (VIO) problem by introducing tightly-coupled fusion of magnetometer measurements. A sliding-window of keyframes is optimized by minimizing the reprojection errors, relative inertial errors, and relative magnetometer orientation errors. The results of IMU orientationpropagation are used to efficiently transform magnetometer measurements between frames, producing relative orientation constraints between consecutive frames. The soft and hard iron effects are calibrated using an ellipsoid fitting algorithm. Introducing magnetometer data results in significant reductions of the orientation error and also in recovering the true yaw orientation with respect to the magnetic north. The proposed framework operates in all environments with slow-varying magnetic fields, mainly outdoors and underwater. We have focused our work in the underwater domain, especially in underwater caves as the narrow passage and turbulent flow makes it difficult to perform loop closures and reset the localization drift. Underwater caves present the most challenging domain due to the absence of ambient light and the confined nature of the environment, while also being a crucial source of fresh water and providing valuable historical records. Experimental results from inside underwater caves demonstrate the improvements in accuracy and robustness introduced by the proposed VIO extension.