Pursuit of "X-Ray Vision" for Augmented Reality

The ability to visualize occluded objects or people offers tremendous potential to users of augmented reality (AR). This is especially true in mobile applications for urban environments, in which navigation and other operations are hindered by the urban infrastructure. This "X-ray vision" feature has intrigued and challenged AR system designers for many years, with only modest progress in demonstrating a useful and usable capability. The most obvious challenge is to the human visual system, which is being asked to interpret a very unnatural perceptual metaphor. We review the perceptual background to understand how the visual system infers depth and how these assumptions are or are not met by augmented reality displays. In response to these challenges, several visualization metaphors have been proposed; we survey these in light of the perceptual background. Because augmented reality systems are user-centered, it is important to evaluate how well these visualization metaphors enable users to perform tasks that benefit from X-ray vision. We summarize studies reported in the literature. Drawing upon these analyses, we offer suggestions for future research on this tantalizing capability.