The term augmented reality was coined in 1992 in the context of developing AR system for assisting aircraft manufacturing (Caudell & Mizell, 1992). Milgram, Takemura, Utsumi and Kishino (1994) have presented a widely used illustration of mixed reality on the reality-virtuality continuum (Figure 1), which describes the position of AR in relation with real and virtual environments. Fairly consistent with Milgram’s continuum, in a well-known research article by Azuma (1997) AR is seen more as supplement to reality, rather than a replacement of reality. According to the definition of Azuma et al. (2001), AR system “combines real and virtual objects in a real environment”, “runs interactively, and in real time”, and “registers real and virtual objects with each other”. They also suggest that AR can be related to all senses, even though the majority of the studies on AR seem to focus on the sense of sight. More recently, user-based personalizing, filtering, creating and sharing of content have been mentioned as some of the main elements of present-day AR applications (Billinghurst & Kato, 2002; Nilsson, Johansson & Jönsson, 2009; Wither, DiVerdi & Höllerer, 2009). In this chapter, AR is seen as reflecting digital information with the real world context that the user perceives, thus enhancing the physical environment with digital information in an interactive way.
Reality-virtuality continuum (Milgram et al. 1994)