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2 State of the Art

In the introduction, we concluded that innovative teaching methodologies have to be adopted to be capable of imparting experienced knowledge to students. Thus, virtual reality teaching and learning approaches will be examined in the following.

Nowadays, an exhaustive number of applications can be found that make use of immersive elements within real-world scenarios. However, the immersive character of all these applications is based on two characteristics of the simulation: The first one is the quality of the three-dimensional representation; the second one is the users identification with the avatar within the virtual world scenario.

The modeling quality of the three-dimensional representation of a virtual scenario is very important in order to be surrounded by a virtual reality that is realistic or even immersive. However, a high-quality graphical representation of the simulation is not sufficient for an intensive experience. Thus, according to Wolf and Perron [17], the following conditions have to be fulfilled in order to enable an immersive user experience within the scenario: Three conditions create a sense of immersion in a virtual reality or 3-D computer game: The users expectation of the game or environment must match the environments conventions fairly closely. The users actions must have a non-trivial impact on the environment. The conventions of the world must be consistent, even if they dont match those of the metaspace.

The users identification with virtual scenario is rather independent from the modeling of the environment. It is also depending on the users empathy with the avatar. Generally, an avatar is supposed to represent the user in a game or a virtual scenario. However, to fulfill its purposes according to the users empathy, the avatar has to supply further characteristics. Accordingly, Bartle defines an avatar as follows: An avatar is a players representative in a world. [] It does as it's told, it reports what happens to it, and it acts as a general conduit for the player and the world to interact. It may or may not have some graphical representation, it may or may not have a name. It refers to itself as a separate entity and communicates with the player.

There are already many technical solutions that are primarily focused on the creation of high-quality and complex three-dimensional environments, which are accurate to real-world scenarios in every detail. Flight Simulators, for example, provide vehicle tracking [18]. Thus, the flight virtual reality simulator is capable of tracking the locomotion of a flying vehicle within the virtual world, but does not take into account the head position of the user. Another VR simulator is the Omnimax Theater, which provides a large angle of view [19], but does not enable any tracking capabilities whatsoever. Head-tracked monitors were introduced by Codella et al. [20] and by Deering [21]. These special monitors provide an overall tracking system, but provide a rather limited angle of view [18]. The first attempt to create virtual reality in terms of a complete adjustment of the simulation to the users position and head movements was introduced with the Boom Mounted Display by McDowall et al. [22]. However, these displays provided only poor resolutions and thus were not capable of a detailed graphical representation of the virtual environment [23].

In order to enable an extensive representation of the aimed remote laboratories, we are looking for representative scenarios that fit to immersive requirements using both a detailed graphical modeling as well as a realistic experience within the simulation. In this context, one highly advanced visualization technology was realized through the development of the Cave in 1991. In this context, the recursive acronym CAVE stands for Cave Automatic Virtual Environment [18] and was first mentioned in 1992 by Cruz-Neira [24]. Interestingly, the naming of the Cave is also inspired by Platos Republic [25]. In this book, he discusses inferring reality (ideal forms) form shadows (projections) on the cave wall [18] within The Smile of the Cave.

By making use of complex projection techniques combined with various projectors as well as six projection walls arranged in form of a cube, the developers of the Cave have redefined the standards in visualizing virtual reality scenarios. The Cave enables visualization techniques, which provide multi-screen stereo vision while reducing the effect of common tracking and system latency errors. Hence, in terms of resolution, color and flicker-free stereo vision the founders of the Cave have created a new level of immersion and virtual reality.

The Cave, which serves the ideal graphical representation of a virtual world, brings us further towards true Virtual Reality, which according to Rheingold [26] is described as an experience, in which a person is surrounded by a three-dimensional computer-generated representation, and is able to move around in the virtual world and see it from different angles, to reach into it, grab it and reshape it. This enables various educational, but also industrial and technical applications. Hence, in the past the research already focused on the power of visualization in technical applications, e.g. for data visualizations purposes [27] or for the exploration and prototyping of complex systems like the visualization of air traffic simulation systems [28]. Furthermore, the Cave has also been used within medical or for other applications, which require annotations and labeling of objects, e.g. in teaching scenarios [29].

The founders of the Cave choose an even more specific definition of virtual reality: A virtual reality system is one which provides real-time viewer-centered headtracking perspective with a large angle of view, interactive control, and binocular display. [18] Cruz-Neira also mentions that according to Bishop and Fuchs [30] the competing term virtual environment (VE) has a somewhat grander definition which also correctly encompasses touch, smell and sound. Hence, in order to gain a holistic VR experience, more interaction within the virtual environment is needed.

Though, it is our aim to turn Virtual Reality into a complete representation of a virtual environment by extending the needed interaction capabilities, which are, together with the according hardware, necessary to guarantee the immersion of the user into the virtual reality [31]. However, even the Cave has got restricted interaction capabilities as the user can only interact within the currently demonstrated perspectives. Furthermore, natural movement is very limited, as locomotion through the virtual environment is usually restricted to the currently shown spot of the scenario. Yet, natural movements including walking, running or even jumping through virtual reality are decisive for a highly immersive experience within the virtual environment.

This gap of limited interaction has to be filled by advanced technical devices without losing high-quality graphical representations of the virtual environment. Hence, within this publication, we introduce the Virtual Theatre, which combines the visualization and interaction technique mentioned before. The technical setup and the application of the Virtual Theatre in virtual scenarios are described in the next chapter.

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