A fundamental problem in optical, see-through augmented reality (AR) is characterizing how it affects the perception of spatial layout and depth. This problem is important because AR system developers need to both place graphics in arbitrary spatial relationships with real-world objects, and to know that users will perceive them in the same relationships. Furthermore, AR makes possible enhanced perceptual techniques that have no real-world equivalent, such as x-ray vision, where AR users are supposed to perceive graphics as being located behind opaque surfaces. This paper reviews and discusses techniques for measuring egocentric depth judgments in both virtual and augmented environments. It then describes a perceptual matching task and experimental design for measuring egocentric AR depth judgments at medium- and far-field distances of 5 to 45 meters. The experiment studied the effect of field of view, the x-ray vision condition, multiple distances, and practice on the task. The paper relates some of the findings to the well-known problem of depth underestimation in virtual environments, and further reports evidence for a switch in bias, from underestimating to overestimating the distance of AR-presented graphics, at 23 meters. It also gives a quantification of how much more difficult the x-ray vision condition makes the task, and then concludes with ideas for improving the experimental methodology.

To achieve accurate registration, the transformations which locate the tracking system components with respect to the environment must be known. These transformations relate the base of the tracking system to the virtual world and the tracking system's sensor to the graphics display. In this paper we present a unified, general calibration method for calculating these transformations. A user is asked to align the display with objects in the real world. Using this method, the sensor to display and tracker base to world transformations can be determined with as few as three measurements.

A useful function of augmented reality (AR) systems is their ability to visualize occluded infrastructure directly in a user's view of the environment. This is especially important for our application context, which utilizes mobile AR for navigation and other operations in an urban environment. A key problem in the AR field is how to best depict occluded objects in such a way that the viewer can correctly infer the depth relationships between different physical and virtual objects. Showing a single occluded object with no depth context presents an ambiguous picture to the user. But showing all occluded objects in the environments leads to the "Superman's X-ray vision" problem, in which the user sees too much information to make sense of the depth relationships of objects. Our efforts differ qualitatively from previous work in AR occlusion, because our application domain involves far-field occluded objects, which are tens of meters distant from the user. Previous work has focused on near-field occluded objects, which are within or just beyond arm's reach, and which use different perceptual cues. We designed and evaluated a number of sets of display attributes. We then conducted a user study to determine which representations best express occlusion relationships among far-field objects. We identify a drawing style and opacity settings that enable the user to accurately interpret three layers of occluded objects, even in the absence of perspective constraints.

We describe two engineering experiments designed to evaluate the effectiveness of Measurand's ShapeTape for wearable, mobile interaction. Our initial results suggest that the ShapeTape is not appropriate for interactions which require a high degree of accuracy. However, ShapeTape is capable of reproducing the qualitative motion the user is performing and thus could be used to support 3D gesture-based interaction.

The full power of mobile augmented and virtual reality systems is realized when these systems are connected to one another to immersive virtual environments, and to remote information servers. Connections are usually made through wireless networks. However, wireless networks cannot guarantee connectivity and their bandwidth can be highly constrained. The authors present a robust event-based data distribution mechanism for mobile augmented reality and virtual environments. It is based on replicated databases, pluggable networking protocols, and communication channels. We demonstrate the mechanism in the Battlefield Augmented Reality System (BARS) situation awareness system, which is composed of several mobile augmented reality systems, immersive and desktop-based virtual reality systems, a 2D map-based multi-modal system, handheld PCs, and other sources of information.