Synchronization of External Inertial Sensors and Built-in Camera on Mobile Devices

The fusion of inertial and visual data is an effective approach to human motion analysis, with applications in areas such as sports or rehabilitation exercise monitoring. Employing wireless, low-cost, external inertial sensors and a built-in camera on mobile devices provides a convenient acquisition system, available for wide range of potential users. In order to take advantage of both data modalities, robust time synchronization is required. We consider consumer-grade devices, for which direct access to internal clocks is not available and only high-level API is provided. At the same time, we aim to avoid event-based synchronization that would require additional user actions. We investigate sources of acquisition errors on mobile devices, and then we propose and evaluate a novel synchronization method for inertial and visual data. Experimental results indicate that the proposed method provides robust synchronization.