Technical Update  

VR is having a ball

A new approach to virtual reality promises to be the most realistic so far. Tom Shelley reports

A virtual world can be projected onto the surface of a large, rotating translucent ball, providing a truly realistic environment to the user.

Within the ball, users can move about in any direction without the restriction of a head set or the danger of hitting a wall. Target customers are the military, process industries and anyone who wishes to examine interactions between human beings and the surroundings in which they live, work, and have to survive.

The goal is to provide a more realistic virtual world in which people can truly walk or even run through, instead of sitting at a desk in front of a workstation screen or in a theatre-type environment.

Julian Eyre, and his small company, VR Systems UK, have just completed their first virtual reality rotating ball environment, in a converted cowshed near Romsey in Hampshire. The ball, given the name Cybersphere, is 3.5m in diameter and made up from two layers of 30 polycarbonate segments. Each segment is 3mm thick, and interlocks with the next by being shaped like a large piece of jigsaw puzzle. The two layers, one inside the other, overcome the problems of joins between the segments. The user stands, or otherwise moves around inside, rotating the ball as he or she moves. Images of the virtual world are projected onto the translucent sides of the ball. In the present configuration, one projector is above, and four are aimed at the sides. The ball rides on an air bearing support, in order to eliminate friction.

Eyre would have liked the ball to be thicker and more rigid but this would have made the ball even heavier: it already weighs 270kg and presents about twice the inertia of a man starting or stopping walking. The present project is essentially a demonstration of feasibility, supported by a DTI Smart Award. Future implementations might include a servo drive system, which would track the motion of the user and rotate the ball appropriately, but this would add a whole new level of cost and complexity not covered by the present funding.

The segments are joined by countersunk screws in tapped holes, but this is also not ideal for long term use. The engineering of the entrance hatch has proved a particular problem. In the present design, the hatch is screwed into place.

The original idea for supporting the ball was to mount it on mechanical bearings, but it soon became apparent that air support would be better. Mechanical bearings were likely to damage the surfaces of the polycarbonate and increase friction and resistance to motion. There would also have been problems supporting the ball, which, because of its thinness, is fairly flexible.

A simple fan, such as might be used to support the interior of inflatable buildings, has proved satisfactory. Only 0.12psi (0.8kPa) air pressure is required to lift the ball clear of its rubber ring support. Sprung wheels help keep the ball central, and prevent the sort of oscillation and pendulation problems associated with balloons.

Movement is detected by having another beach ball sized ball pressed against the underside. Wheels arranged at 90E to each other press against the outside of the second ball to pick up movement, and transmit it to the controlling computer using conventional tracker ball software. The second ball is supported by three 60mm tracker balls.

Segments were made by vacuum forming sheet over a coated glass fibre tool, and then CNC cutting them to shape, while retaining suction. Considerable problems were experienced in getting the geometry correct, and even now, it can be seen that the fit between segments is not perfect. This was exacerbated by the natural tendency of the ball to distort under its own weight during construction.

The images projected onto the outside of the ball must be distorted to compensate for the geometry. Compared to a conventional image, the images have to be barrel distorted (that is, squeezed at the edges and expanded in the centre). The company has devised an optical method of doing this, but is also in conversation with Equipe in Worthing. Equipe produces solutions for flight simulation and similar applications, based on Silicon Graphics Infinite Reality Graphics software, and running on the same company's hardware. Further digital processing is needed in order to merge the edges of the projected images.

The nearest anyone has come to achieving this level or reality hitherto is the American Cave system, in which users can move about a room in which three walls show back-projected images of the simulated virtual world. A head tracking system automatically compensates for parallax. While superb for entertainment and vehicle mock-ups, real human-machine, human-process plant and human-environment interactions are limited by the walls. The alternatives are to put on a headset with eye screens, or sit in a Reality Centre type wrap around cinema screen environment. Despite the expense of these systems, engineers are finding them very useful for design review meetings; the UK arm of Silicon Graphics has now sold 14 Reality Centres as well as renting out its original facility in Theale on a host of occasions.

VR Systems is looking for partners with whom it can take the technology further and turn it into a commercial product. Potential customers include the offshore, process and plant industries, who may want to realistically simulate moving around inside an environment, especially under emergency conditions. Maintenance tasks on aircraft engines and other major pieces of machinery can also potentially be studied more realistically than at present. The police, fire fighters and the military are also likely to find it of benefit in studying and simulating different scenarios. Even estate and travel agents may want it to show clients round properties and locations expensive to visit, or which have not yet been built. Uses in the entertainment industry should be obvious.


Design Pointers
Rotating ball concept allows users to experience virtual reality under more realistic conditions in which they can roam and move around without limit

The project is now in the feasibility phase, rather than a prototype system, although it should soon be at the point where it can be put to serious practical use

Costs of complete systems are likely to be closely comparable with present multi projector Reality Centre systems, whose prices have dropped considerably since the first one was built


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