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Aviation History
1993
1993 - 0085.PDF
Barrette, allowing a daylight scene compris ing 1,250 surfaces, but no lights. Lightpoints are typically 60% calligraphic — used for bright, sharp runway lights — and 40% raster. Full-colour phototexture patterns can be applied to all surfaces in the scene to enhance realism. MaxVue has a large online texture memory of 24 million texture cells — enough to store 379 different patterns, each comprising 256 x 256 "texels" — a capacity Barrette compares with high-performance military mission-rehearsal visuals such as the Evans & Sutherland ESIG-4000 and GE Aerospace Compu-Scene VI. The texture memory is actually 50% bigger than stated to allow for storage for up to ten levels of detail, ranging in resolution from 64 x 64 texels to 1,024 x 1,024, for each pattern. These "MIP maps" are used to control scene content, to avoid overloading the image generator while al lowing feature details to appear smoothly as objets get closer. Phototexture patterns can be generic or specific. CAE's database-preparation system can be used with almost any source mate rial, starting with 1:50,000 maps and pro gressing through satellite images — 30m- resolution Landsat, 10m Spot and 5m Soyuzkarta — to aerial photographs with better than 0.5m resolution and, finally, to hand-held photographs of airport buildings, vehicles and airliner logos. A typical airport database has one satellite, 16 aerial and 24 hand-held photographs, says CAE. Maps are digitised and images are scanned into the system. The database is built up in layers, starting with the terrain, followed by culture polygons and finally three-dimensional objects and lighting. Sat ellite images provide the "supercoarse" and coarse phototexturing for high-altitude fly ing, with higher-definition images used for the higher-resolution patterns needed at lower altitudes. Barrette highlights MaxVue's low trans port delay — the time taken for the visual to respond to simulator movement and a measure of fidelity. The delay is under 60ms in 50Hz daylight mode and under 103ms in 30Hz dusk/night mode — at least 10ms faster than other commercial visuals, he says, also noting that "...simulators are getting faster". Usually, a visual is not synchronised with its simulator and can be up to one image frame behind. MaxVue has the "unique" ability to be synchronised with the simula tor host computer to increase fidelity, says Barrette. The visual runs at 30Hz in dusk/ night mode, and can be synchronised with the simulator running at 60Hz. The visual can run at 60Hz in daylight mode, to be synchronised with the simulator, but poly gon power is reduced. In unsynchronised mode, the frame length can be stretched a few milliseconds to give the image generator more time to Computer power and human ingenuity recreate a German village on ESIG-4000 Visuals for fighting or fun Image-generator technology is driven up wards by the demands on visual systems for military simulators. Image-generator prices are being driven downwards by the emerging entertainment market. Phototexture was introduced on high- cost, high-performance image generators for military training and engineering re search. This method of enhancing scene realism is now standard on commercial flight-simulator visuals and is available even on low-cost image generators. Evans & Sutherland (E&S) is develop ing the ESIG-4000 high-performance image generator to enable US Air Force Special Operations Forces aircrew to re hearse covert missions in the simulator over terrain which exactly matches what they will see on the real mission. To accomplish this feat, E&S has had to develop new image-generation tech niques, such as the theme-cell, or themel. This is used where there is no photo graphic source data, or where the texture resolution over large areas of the visual database is too low to be useful. The image generator uses digital fea ture-codes which identify areas of the database simply as forest, fields or houses, for example. These codes call up generic, but highly detailed, "photo-typical" tex ture motifs. Themels can include numer ous three-dimensional objects, such as houses, and create a scene so dense that the pilot "...can no longer fly between the trees", says E&S. Themels are one example of techniques which will find their way into commercial visuals and ultimately into the new, but potentially enormous, entertainment mar ket. With machines such as E&S's ESIG- 2000, General Electric's SE 1000 and Silicon Graphics' Reality Engine all priced under $100,000, the entertainment indus try is no longer deterred by price. GE has signed a deal with Sega to enhance the visuals used in arcade com puter-games, while E&S has a joint pro ject with Iwerks Entertainment to develop a "virtual reality" attraction called Virtual Adventures. Forecasts of demand for image generators for entertainment use are measured in billions of dollars and could transform the visuals industry. FLIGHT INTERNATIONAL 20 - 26 January, 1993 31
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