Technology: Computer graphics learns rules of the game


By ELISABETH GEAKE Designers on opposite sides of the world will soon be able to work on the same 3-D computer model using ordinary personal computers linked by ordinary phone lines, rather than powerful graphics workstations. Software being developed at the Guildford research centre of the Japanese company Canon reduces the amount of data needed to display 3-D objects on a computer screen. The reduction is such that images of moving objects changing ten times a second can be sent down phone lines. Graphics workstations are normally needed to display moving 3-D objects because of the huge number of calculations needed to work out which objects are nearest to the viewer and cover up those further away. Three coordinates, x, y and z, represent each point of an object. z represents the distance into the screen, and is stored in a memory called the z buffer. When the computer displays a table in front of a wall, for example, it compares the z buffer values to find out which should appear in front of the other. This has to be done for every pixel (or dot) on the screen, and there are more than 300 000 on many computer monitors. If an object is moving, all the calculations have to be done several times a second. Adam Billyard, the inventor of Canon Interactive Graphics (CIG), used to write computer games, which demand very economical use of data to keep down costs. He decided it would be quicker to group the pixels; if part of the table is in front of the wall, all of it must be. This slashes the number of calculations needed. Graphics workstations which use z buffers have extra silicon chips to speed them up. But CIG uses very little data, so needs no extra chips and can be run on almost any desktop computer. Billyard and his colleague Richard Haddy began work in March 1991, and the software may be available some time next year. It all fits on one floppy disc, and the faster the computer it is used on, the faster it works. Billyard says that each change to a scene takes about 100 bytes of data, and at least 10 updates a second are needed for a moving image. This is about the same data rate as a modern fax machine achieves. Canon’s researchers have not tried a phone link yet, but they believe it will be possible to do so. They say there are methods of coping with phone delays and two people trying to change the same thing in different ways simultaneously. David Lau-Kee, the project leader, says that CIG uses so little of the computer’s processing power that it is possible to do other things at the same time. For example, the computer could carry out scientific calculations while also showing the results as a 3-D graph. Even experts find it difficult to compare graphics software. Inter-graph, a computer-aided design company, says one of its computers can draw pictures containing 50 000 polygons in one second, but Canon claims its CIG can draw 80 000 polygons in a second with a computer that is 20 per cent slower – though Canon polygons are not necessarily identical to Inter-graph ones. Intergraph recently launched a CAD Conferencing system so that designers far apart can work together,
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