A lightweight and scalable visual-inertial motion capture system using fiducial markers

Accurate localization of a moving object is important in many robotic tasks. Often an elaborate motion capture system is used to realize it. While high precision is guaranteed, such a complicated system is costly and limited to specified small size workspace. This paper describes a lightweight and scalable visual-inertial approach, which leverages paper printable, known size and unknown pose, artificial landmarks, as called fiducials, to obtain motion state estimates, including pose and velocity. Visual-inertial joint optimization using incremental smoother over factor graph and the IMU preintegration technique make our method efficient and accurate. No special hardware is required except a monocular camera and an IMU, making our system lightweight and easy to deploy. Using paper printable landmarks, as well as the efficient incremental inference algorithm, renders it nearly constant-time complexity and scalable to large-scale environment. We perform an extensive evaluation of our method on public datasets and real-world experiments. Results show our method achieves accurate state estimates and is scalable to large-scale environment and robust to fast motion and changing light condition. Besides, our method has the ability to recover from intermediate failure.