Ubiquitous tracking setups, covering large tracking areas with many heterogeneous sensors of varying accuracy, require dedicated middleware to facilitate development of stationary and mobile applications by providing a simple interface and encapsulating the details of sensing, calibration and sensor fusion.In this paper we present a centrally coordinated peer-to-peer architecture for ubiquitous tracking, where a server computes optimal data flow configurations for sensor and application clients, which are directly exchanging tracking data with low latency using a lightweight data flow framework. The server's decisions are inferred from an actively maintained central spatial relationship graph using spatial relationship patterns.The system is compared to a previous Ubitrack implementation using the highly distributed DWARF middleware. It exhibits significantly better performance in a reference scenario.
MOTIVATIONIn industrial augmented reality scenarios, there is a growing demand for integrated working environments which span large factory buildings. In such an environment, many different mobile and stationary AR-supported applications, such as logistics, production, maintenance or factory planning may coexist and require shared access to permanent tracking with varying accuracy requirements. Today, no single technology exists that satisfies the tracking requirements of all these applications and can -at least for a reasonable price -be deployed throughout such an environment. For this reason, in a realistic setup, many different tracking systems would be installed ranging from low-precision wide-area WLAN tracking to infrared-optical systems covering only small areas with high accuracy. The installation, maintenance and expansion of such a largescale heterogeneous tracking environment poses new challenges to the underlying middleware concepts.Heterogeneous wide-area tracking environments Emerging tracking methods based on technologies like WLAN or RFID provide the possibility to deploy tracking to ever-enlarging indoor areas. With increasing tracker coverage, a larger diversity of AR applications will need to share this tracking infrastructure. Stationary applications that are already in use will more and more be complemented by mobile applications that would have been completely impossible without wide-area tracking. Also, applications that are stationary today, might benefit from enlarging tracking areas and * e-mail: { huberma, pustka, keitler, echtler, klinker }@in.tum.de become more adaptive and better integrated in the productive environment. Many of these wide-area tracking systems have the drawback of being rather imprecise. Nevertheless, they serve quite well for navigation problems and can thereby bridge the gap between islands of higher tracking accuracy. Furthermore, they can provide useful initial positions to other sensors, such as markerless optical trackers [7]. There are also many examples where a fusion of measurements from different mobile and stationary sensors improves overall trac...