Optical outside-in tracking using unmodified mobile phones

Marker-based optical outside-in tracking is a mature and robust technology used by many AR, VR and motion capture applications. However, in small environments the tracking cameras are often difficult to install. An example scenario are ergonomic studies in car manufacturing, where the motion of a worker needs to be tracked in small spaces such as the trunk of a car. In this paper, we describe how to extend the tracking volume in small, cluttered environments using small and flexible wireless cameras in form of unmodified mobile phones that can quickly be installed. Since those small cameras are not synchronized with the main tracking cameras, we describe several modifications to the tracking algorithms, such as inter-frame interpolation, the replacement of the least-squares adjustment by a Kalman filter and the integration of rolling-shutter compensation. To support the quick setup of additional cameras while the tracking system is running, the system is extended by an on-line calibration technique that determines the extrinsic camera parameters without requiring a dedicated calibration step.