Revisiting Visual-Inertial Structure-From-Motion for Odometry and SLAM Initialization

In this letter, an efficient closed-form solution for the state initialization in visual-inertial odometry (VIO) and simultaneous localization and mapping (SLAM) is presented. Unlike the state-of-the-art, we do not derive linear equations from triangulating pairs of point observations. Instead, we build on a direct triangulation of the unknown 3D point paired with each of its observations. We show and validate the high impact of such a simple difference. The resulting linear system has a simpler structure and the solution through analytic elimination only requires solving a 6 × 6 linear system (or 9 × 9 when accelerometer bias is included). In addition, all the observations of every scene point are jointly related, thereby leading to a less biased and more accurate solution. The proposed formulation attains up to 50 percent decreased velocity and point reconstruction error compared to the standard closed-form solver, while it is 4× faster for a 7-frame set. Apart from the inherent efficiency, fewer iterations are needed by any further non-linear refinement thanks to better parameter initialization. In this context, we also present a non-linear optimizer that optionally refines the initial parameters. The superior performance of the proposed solver is established by quantitative comparisons with the state-of-the-art solver.