What is augmented reality? An AR system supplements the real world with virtual (computer-generated) objects that appear to coexist in the same space as the real world. While many researchers broaden the definition of AR beyond this vision, we define an AR system to have the following properties: (1) combines real and virtual objects in a real environment; (2) runs interactively, and in real time; and (3) registers (aligns) real and virtual objects with each other. Note that we don t restrict this definition of AR to particular display technologies, such as a headmounted display (HMD). Nor do we limit it to our sense of sight. AR can potentially apply to all senses, including hearing, touch, and smell. Certain AR applications also require removing real objects from the perceived environment, in addition to adding virtual objects. For example, an AR visualization of a building that stood at a certain location might remove the building that exists there today. Some researchers call the task of removing real objects mediated or diminished reality, but we consider it a subset of AR. Milgram defined a continuum of real-to-virtual environments, in which AR is one part of the general area of mixed reality (Figure 1). In both augmented virtuality, in which real objects are added to virtual ones, and virtual environments (or virtual reality), the surrounding environment is virtual, while in AR the surrounding environment is real. We focus on AR and don t cover augmented virtuality or virtual environments.
