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3 The Virtual Theatre Enabling Virtual Reality in Action

The Virtual Theatre was developed by the MSEAB Weibull Company [32] and was originally carried out for military training purposes. However, as discovered by Ewert et al. [33], the usage of the Virtual Theatre can also be enhanced to meet educational requirements for teaching purposes of engineering students. It consists of four basic elements: The centerpiece, which is referred to as the omnidirectional treadmill, represents the Virtual Theatres unique characteristics. Besides this moving floor, the Virtual Theatre also consists of a Head Mounted Display, a tracking system and a cyber glove. The interaction of these various technical devices composes a virtual reality simulator that combines the advantages of all conventional attempts to create virtual reality in one setup. This setup will be described in the following.

The Head Mounted Display (HMD) represents the visual perception part of the Virtual Theatre. This technical device consists of two screens that are located in a sort of helmet and enable stereo vision. These two screens one for each eye of the user enable a three-dimensional representation of the virtual environment in the perception of the user. HMDs were first mentioned in Fisher [34] and Teitel [35] as devices that use motion in order to create VR. Hence, the characteristic of the HMD consists in the fact that it has a perpendicular aligned to the user and thus adjusts the representation of the virtual environment to him. Each display of the HMD provides a 70 stereoscopic field with an SXGA resolution in order to create a gapless graphical representation of the virtualized scenario [33]. For our specific setup, we are using the Head Mounted Display from zSight [36]. An internal sound system in the HMD enables an acoustic accompaniment for the visualization to complete the immersive scenario.

As already mentioned, the ground part of the Virtual Theatre is the omnidirectional treadmill. This omnidirectional floor represents the navigation component of the Virtual Theatre. The moving floor consists of rigid rollers with increasing circumferences and a common origo [33]. The rotation direction of the rollers is oriented to the middle point of the floor, where a circular static area is located. The rollers are driven by a belt drive system, which is connected to all polygons of the treadmill through a system of coupled shafts and thus ensures the kinematic synchronization of all parts of the moving floor. The omnidirectional treadmill is depicted in figure 1.

Fig. 1. Technical design of the Virtual Theatres omnidirectional treadmill

On the central area that is shown in the upper right corner of figure 1, the user is able to stand without moving. As soon as he steps outside of this area, the rollers start moving and accelerate according to the distance of his position to the middle part. If the user returns to the middle area, the rotation of the rollers stops.

The tracking system of the Virtual Theatre is equipped with ten infrared cameras that are evenly distributed around the treadmill in 3 m above the floor. By recording the position of designated infrared markers attached to the HMD and the hand of the user, the system is capable of tracking the users movements [33]. Due to the unsymmetrical arrangement of the infrared markers the tracking system is not only capable of calculating the position of the user, but is also capable of determining looking directions. That way, the three-dimensional representation of the virtual scenario can be adjusted according to the users current head position and orientation. Furthermore, the infrared tracking system is used in order to adjust the rotation speed of the rollers no only according to the users distance from the middle point, but also according to the difference of these distances within a discrete time interval. Using these enhanced tracking techniques, the system can deal with situations, in which the user stands without moving while not being located in the middle of the omnidirectional floor.

The cyber glove ensures the tactile interaction capabilities. This special hand glove is equipped with 22 sensors, as indicated above, which are capable of determining the users hand position and gestures [33]. This enables the triggering of gesture based events like the grasping of objects. Additionally, special programmable gestures can be utilized in order to implement specific interaction commands.

After setting up the required hardware of the Virtual Theatre, the user can plunge into different scenarios and can be immersed by virtual reality. After the development of learning and interaction scenarios as described in [16], our main interest here is focused on the development of remote laboratories, which represent the first step towards the realization of a virtual factory. The development, testing and evaluation of our first Remote Lab are described in the next chapter.

 
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