SOFT2: Stereo Visual Odometry for Road Vehicles Based on a Point-to-Epipolar-Line Metric

Accurate localization constitutes a fundamental building block of any autonomous system. In this article, we focus on stereo cameras and present a novel approach, dubbed SOFT2, that is currently the highest-ranking algorithm on the KITTI scoreboard. SOFT2 relies on the constraints imposed by the epipolar geometry and kinematics, i.e., it is developed for configurations that cannot exhibit pure rotation. We minimize point-to-epipolar-line distances, which makes the approach resilient to object depth uncertainty, and as the first step, we estimate motion up to scale using just a single camera. Then, we propose to jointly estimate the absolute scale and the extrinsic rotation of the second camera in order to alleviate the effects of varying stereo rig extrinsics. Finally, we smooth the motion estimates in a temporal window of frames by using the proposed epipolar line bundle adjustment procedure. We also introduce a multiple hypothesis feature-matching approach for self-similar planar surfaces that account for appearance change due to perspective. We evaluate SOFT2 and compare it to ORB-SLAM2, OV2SLAM, and VINS-FUSION on the KITTI-360 dataset, KITTI train sequences, Malaga Urban dataset, Oxford Robotics Car dataset, and Multivehicle Stereo Event Camera dataset.