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Section 2: Virtual Reality: History, Philosophy and Theory#

2.3 Flexibility and interaction#

Video or paintings can be used to represent certain limited conditions, but a computer-based model is theoretically unbounded. For example, the same model of an airport may be viewed under a variety of programmed conditions (bad weather, night-time etc.). The scope for designing worlds, and the objects within them, is limitless as real-world constraints, such as gravity, dimension or even common sense, do not have to apply.

Whilst VR can present realistic scenarios, it can also be used to present scenarios that otherwise would be impossible to experience. A developer could construct a rocket for travel to distant galaxies, or reconstruct the streets of ancient Pompeii. Theoretically such boundless opportunity is available in any graphics medium, dependent only on the skill and imagination of the illustrator. The power of VR is that it can take the created world, real or fantastic, and allow a user to interact with it. Interactivity is one of the core elements of VR and separates it from other two- and three-dimensional graphics mediums. VR can allow one or many people to interact with computer-generated objects and worlds in the way that they would interact with the real-world (or other) equivalents. Users can apparently fly to distant galaxies or, if they so wish, stand on the streets of Pompeii just before Vesuvius erupts!

The degree of interaction that users have in a VR world depends loosely on engineering within the world itself and the hardware that they use to interact with it. A VR world is effectively an interface that gives users some feeling of existence within an artificial world created by computer graphics (Vellon et al. 1999). Users may be represented in the world in a range of forms: as a complete virtual body (an avatar), as a part of a body such as a hand or as a controllable viewpoint (Shawver 1997). The world can be engineered to give users control of elements within it, for example a vehicle, and navigation can be enhanced by including three-dimensional signposts, instruments or buttons. It is also possible to add text or other two-dimensional graphic aids to a VR world to assist users in their tasks.

A variety of visualisation systems and external hardware devices are used to enable interactions with VR worlds. The level of 'immersion' within a world is dependent upon the devices that are used, and the sort of interactivity that is designed into the world. The most common systems for viewing VR worlds can be summed up as:

  • Projected. The user's field of vision is effectively filled by screens displaying a projected virtual world. Projection may be onto large concave screens in front of the user or within 'caves' or 'sheds' that users walk into. The latter can fill a 360 degree field of vision
  • Headsets. Users wear stereoscopic glasses or head-mounted displays (HMDs) which place small screens right in front of their eyes. HMDs enhance users' feeling of immersion/interaction within a world by excluding any glimpse of the real world and by revising the view of the virtual world as the user moves their head to look around
  • Desk-top. The virtual world is projected onto the screen of a standard computer monitor. This approach relies on interactive features built into the world to provide a degree of immersion for users
  • Table-top. The virtual world is projected onto a horizontal table-top screen, and is otherwise similar to the desk-top display. It allows interaction in circumstances where a horizontal format is appropriate. For example, a mechanic could learn how to fix a virtual machine in a way that simulates working on a real table-top.

Specialist hardware devices are available that can give users a greater sense of immersion within the world. These devices include the HMD (Barfield et al. 1997) and sensor or data-gloves, which are designed to allow natural movements of the head or the hands in the real world to control movements in a virtual world. However, the standard computer keyboard, mouse, joystick or the more VR-specific spaceball (Jern and Earnshaw 1995) can enable a user to control a vehicle, avatar, tool or viewpoint and offer a level of immersion within a virtual world.

The different levels of immersion within virtual worlds can be defined as:

  • Fully Immersive. An array of VR specific hardware is used to translate a user's natural movements into virtual activity. Devices include the HMD (described above), sensor or data-gloves and sensors attached to a user's body that detect, and translate, real movement into virtual activity (Cress et al. 1997). Devices can also be designed to give users feedback from the virtual world, for example sensations can be stimulated on the skin (e.g. heat or cold) or gloves can physically resist movement when a virtual object is encountered (Luecke and Chai 1997)
  • Partially Immersive. The hardware that is used in these systems allows users to remain aware of their real-world surroundings rather than being fully immersed in the virtual world. For example, a partially immersive system may include a sensor-glove and a virtual hand but use a desk-top screen for visualisation. In this case, users are fully aware of their surroundings but can interact with the world with natural movements using the glove. Desk-top systems which allow users to control movements using a standard mouse offer a lesser degree of immersion
  • Augmented. In augmented reality systems, users have access to a combination of VR and real-world attributes by superimposing graphical information over the real-world (Kim et al. 1997]. For example, a trainee surgeon could perform an operation on a virtual dummy using HMD or table-top display and a real scalpel. Such a system enables users to develop appropriate motor skills without risk and under a range of different conditions.

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