This paper proposes an ego-motion tracking method that utilizes visual-inertial sensors for wearable blind navigation. The unique challenge of wearable motion tracking is to cope with arbitrary body motion and complex environmental dynamics. We introduce a visual sanity check to select accurate visual estimations by comparing visually estimated rotation with measured rotation by a gyroscope. The movement trajectory is recovered through adaptive fusion of visual estimations and inertial measurements, where the visual estimation outputs motion transformation between consecutive image captures, and inertial sensors measure translational acceleration and angular velocities. The frame rates of visual and inertial sensors are different, and vary with respect to time owning to visual sanity checks. We hence employ a multirate extended Kalman filter (EKF) to fuse visual and inertial estimations. The proposed method was tested in different indoor environments, and the results show its effectiveness and accuracy in ego-motion tracking.
Note to Practitioners-This paper was motivated by the necessary mobility needs of visually impaired and blind people.According to a review, the top listed accidents they experienced were head-level collision and motion collision, even though they were using assistive devices. Currently, assistive devices are available to emulate missed functions due to vision loss, such as text reading, object recognition, and knee-level obstacle avoidance (e.g., smart canes), but they do not provide the solution to the fundamental problems as raised in the review. The research team is developing a wearable blind navigator based on Google Glass. The target function modules include traversable region detection, motion estimation, and scene dynamics analysis. The ego-motion estimation method presented in this paper is part of the motion estimation module. The experiments on real scenarios suggest that this approach is feasible and effective. In future research, we will address the problems of robustness and real-time performance in system implementation.