Vision-Based Tracking for Mobile Augmented Reality

Augmented Reality Systems (ARS) attempt to enhance humans' perception of their indoors and outdoors working and living environments and understanding of tasks that they need to carry out. The enhancement is effected by complementing the human senses with virtual input. For example, when the human visual sense is enhanced, an ARS allows virtual objects to be superimposed on a real world by projecting the virtual objects onto real objects. This provides the human user of the ARS with additional information that he/she could not perceive with his/her senses. In order to receive the virtual input and sense the world around them augmented with real time computer-generated features, users of an ARS need to wear special equipment, such as head-mounted devices or wearable computing gears. Tracking technologies are very important in an ARS and, in fact, constitute one challenging research and development topic. Tracking technologies involve both hardware and software issues, but in this chapter we focus on tracking computation. Tracking computation refers to the problem of estimating the position and orientation of the ARS user's viewpoint, assuming the user to carry a wearable camera. Tracking computation is crucial in order to display the composed images properly and maintain correct registration of real and virtual worlds. This tracking problem has recently become a highly active area of research in ARS. Indeed, in recent years, several approaches to vision-based tracking using a wearable camera have been proposed, that can be classified into two main categories, namely "marker-based tracking" and "marker-less tracking." In this chapter, we provide a concise introduction to vision-based tracking for mobile ARS and present an overview of the most popular approaches recently developed in this research area. We also present several practical examples illustrating how to conceive and to evaluate such systems