Virtual Reality (the creation of entire virtual worlds that can be explored within a computer), has been used in archaeology for many years (see Renfrew 1997). However, the term Virtual Reality now really only covers one aspect of so-called virtuality. As technology has advanced, we are now able to merge computer-generated 'reality' with the real world, creating a Mixed Reality (MR) (Ohta and Tamura 1999). This has lead to the creation of a scale of virtuality – the Reality- Virtuality continuum (Milgram and Colquhoun 1999) – shown in Figure 1. This scale goes from the Real Environment (RE) through Augmented Reality (AR), Augmented Virtuality (AV) to a full Virtual Environment (VE).
The focus for this article is the Augmented Reality (AR) section of the continuum. AR is a blend of the real world with some limited level of augmentation from the virtual world. AR 'allows a user to work in a real world environment while visually receiving additional computer-generated or modelled information to support the task at hand' (Schnabel et al. 2007, 4). This normally involves overlaying the live video feed from a mobile device with virtual objects. It allows new objects to be created and inserted into the real world, but 'still holds the real elements and analog conditions as an indispensable part of its nature' (Ma and Choi 2007, 36). One implication for archaeologists, for example, is that it is now possible to visit an archaeological site with a tablet computer or mobile phone, hold up the device and view the site virtually reconstructed on the video feed, while exploring the site in situ.
ARCHEOGUIDE, released in 2001, is an early example of an AR device used to aid a tourist's experience of an archaeological site. The user is given an AR Head-Mounted Display (HMD) and reconstructions of the ancient buildings are overlaid directly onto the real world. The more recent Cultural Heritage Experiences through Socio-personal interactions and Storytelling (CHESS) project take a similar approach - users are led on a personalised tour through the new Acropolis Museum, with the AR content being delivered through a handheld tablet (Roussou et al. 2013). Christopher Witmore presents a slightly different approach, citing work by the artist Janet Cardiff, in which she supplies the user with a small video camera on which she has loaded a previously recorded tour of a site. The user then attempts 'to synchronize their movements through the same locale with her prerecorded journey by maintaining their pace and carrying a small digital video camera as if they were ﬁlming the same sequence' (Witmore 2004, 61).
George Papagiannakis et al. (2004; 2005; Papagiannakis and Magnenat-Thalmann 2007) produced one of the best-known cultural heritage AR applications, centred on the site of Pompeii. Using a tracked video-see- through Head Worn Device (goggles) and dynamic modelling of the real and virtual world, Papagiannakis and his team were able to insert virtual characters into various buildings within Pompeii and enact a real-time storytelling scenario.
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