The Pursuit of “X-ray Vision” in Augmented Reality
One of the most intriguing capabilities envisioned for augmented reality (AR) systems is the notion of “X-ray vision,” or the ability to virtually “see through” one surface to what in reality is hidden from view. Many AR systems have been premised on this feature for the primary value provided by the application.
There are two sides to this unique perceptual capability. There is the issue of the absolute distance of graphical entities within the coordinate system of the real envi- ronment. There is also the relative order of real and virtual surfaces within the merged environment. Neither of these perceptual capabilities seem to come natu- rally for AR users, and thus numerous visual metaphors have been conceived in order to give the impression of relative and absolute depth.
Developing X-ray vision AR systems is a difficult problem from a number of perspectives. First, X-ray vision is truly an unnatural act. This is not an ability peo- ple perform without the aid of perceptual and cognitive mechanisms, and as such there are few metaphors to which people can relate. Therefore, careful consider- ation of depth cues and their usability, as well as the introduction of new cues, are required. Second, the presentation of X-ray vision information to the user is more difficult than presenting depth in traditional three-dimensional (3D) graphics or even virtual environments (VE). In the latter, there is a rich history of experiments showing that depth is underestimated. This is due to the fact that the system is not in complete control of the visual information received by the user. This chapter will explore the perceptual background, visual metaphors, and empirical investigations into overcoming this challenging and important topic in AR research. We conclude with an analysis of the research and suggestions for further research.