# X-Reality Museums: Unifying the Virtual and Real World Towards Realistic Virtual Museums
## 2 Related Work
### Extended Reality (XR)
Early examples of AV explored the now common practice of texturing 3D surfaces with real-life video and photographs [30]. More recent applications based on efficient, low-cost platforms, include 3D videoconferencing [31], telepresence [32] and infotainment [33], gaming [34; 35], education [36], scene inspection [37; 38], and even surgical operation [39]. In this relatively well-established AR/MR/VR landscape, extended reality (XR)-sometimes also referred to as cross-reality [40]--has been given at least three definitions, as a superset, extrapolation or even subset of MR [41]. In this work, XR refers to the collective range of taxonomies of the reality-virtuality continuum, including AR, MR and VR applications [42]. In this respect, XR aims to fuse layered objects into the real world with an immersive digital world, allowing users to partake in activities that are not possible in a strictly MR digital environment, or even the real physical world. Combined with the various technological advancements in human-computer interaction to act as key enablers, users' experience with AR, MR, and VR applications is enhanced [11], enabling XR to reach beyond \"reality\" (eXtended). This type of intersection between the real and the virtual generates ample opportunities for XR applications to facilitate an entirely new \"reality\" space to interact with and innovate inside of. It represents the next step towards immersive interaction through parallel enabling technologies, to create an advanced experience with real-time rendering requirements. XR focuses on weaving together each enabler's heterogeneous interaction layers so as to deliver a unique experience, one that integrates users in both a physical and a virtual representation of the same geographical space at the same time. Incorporating elements of diminished and mediated reality (e.g., replacing physical objects with virtual ones, as well as realistic character blending, animation techniquesand rendering features) into an XR environment will allow it to be used as a building block for producing various novel augmented, mixed and virtual reality applications. XR encompasses a wide spectrum of hardware and software, including sensory interfaces, applications, and infrastructures, that enable content creation for its subsets, AR, MR, and VR [43]. XR thus represents the convergence of AR, MR, and VR, in which the best elements of each aspect are utilized and optimized for a given use case scenario and application [44]. Representing a crossroads where multidisciplinary research conducted in the fields of computer vision (e.g., body tracking, hands articulation, face detection), artificial intelligence (e.g., natural language processing and generation, conversational systems), graphics (e.g., realistic 3D modelling, rendering, and animation) and natural interaction meet, XR tools have the unique potential to revolutionize cultural heritage experiences in terms of interpretation, visualization and interaction. In this respect, XR aims to replace the real world with an artificially enhanced environment orchestrated by software, and to stimulate in such environments a user's physical presence by duplicating, to the extent possible, the five basic senses of sight, touch and hearing, but also smell and taste, currently addressed at an experimental extent [45]. XR technologies proposed as a vehicle for promoting enhanced cultural experiences will allow people to virtually travel to other areas, and experience local history and lore in a fascinating way. Cultural organisations, as well as agencies engaged in and/or furthering humanitarian efforts, are tapping into the unique potential of AR/MR/VR technologies, in particular the empathy-inducing capabilities of VR [46]. These can effectively educate and raise awareness about certain issues, and even elicit response and action among viewers, as similar effects have been observed in VR-like museum experiences [47].