by Diana Phillips Mahoney
Although the goal of most virtual-reality applications is to create a digital replica of the real world, it turns out that actual reality is not always a high enough standard for its computer-based counterpart. Sometimes, to be useful or effective, a virtual world has to present an altered reality, one in which the perspective of a physical environment has been changed in order to make the application easier to understand or prettier to look at. Such was the irony facing the content solutions group of British VR company Super scape last year, when National Geographic magazine commissioned the company to build a virtual window into the universe.
The magazine presented the Superscape team with a concept for an interactive, 3D representation of the solar system that could serve as a focal point for the magazine's Web site. Each planet was to be visually distinct, incorporating realistic surface textures and colors, as well as characteristic weather patterns, moons, and solar-cycle effects. At the center of the orbiting planets, the sun would project its rays onto the planets and satellites, and the surfaces of those bodies would be lit and shadowed as they are in the real world.
|Jupiter's volcanic moon Io moves in a circular orbit around the planet in an interactive digital solar system created by Superscape for National Geographic's Web site.|
To bring the concept to digital life, the Superscape designers faced a fundamental creative challenge. The charter handed to them by National Geographic called for a realistic digital solar system, but striving for literal realism would make the ap pli ca tion ineffective. "If we used a direct, linear scale model of the solar system, we couldn't have presented the planets simultaneously, unless they were about a pixel in size each. And National Geographic wanted users to be able to see all of the planets at once," says Paul Grimsdale of Superscape, lead programmer on the project.
Consequently, Grimsdale developed separate distance and size scales to define the virtual model so the planets and satellites could be viewed simultaneously in detail. He modeled the interplanetary distances using a logarithmic scale that shows the outermost planets being twice as far from the sun as the Earth, and he used a different logarithmic scale to calculate the relative sizes of the planets and satellites. With these scales, even the smallest bodies that were modeled for the application-Mars satellites Phobos and Dei mos-can be viewed in detail in real time.
In terms of the simulation itself, the orbital periods of the planets are correct relative to one another, but the rate at which virtual time passes is increased. "We've modified the rate so it might take 10 seconds for a planet to spin when you zoom in on it. Otherwise, it would be too slow to notice the motion," says Grimsdale. "It's interesting to zoom into a planet that spins slowly in the real world but which only takes 10 seconds to make a complete revolution [in the virtual world]. All the other planets appear to whiz by. So the user is still getting an idea of the relative orbital rates."
All the data for the planets, including the 2D textures and orbital and weather information, was obtained directly from NASA sources and thus is physically accurate. Even so, the data had to be tweaked to achieve a realistic look. "We had to work with the data to come up with a visual representation that captured its integrity," says Grimsdale. "We spent a lot of time getting a precise mapping of the textures onto the spherical 3D objects and playing around with the lighting and the shading to achieve a realistic effect."
The group took advantage of the then-new advanced shading and lighting enhancements of Superscape's core development engine, VRT, in which all the models were built. "A specification for this proj ect was that it should run on a high-end PC. In fact, the project started out as a way to demonstrate the power of the Pentium III architecture. Some of the new lighting and shading effects we were using would have tied up a standard Pentium II box, generally precluding use on a mainstream Web site," says Grimsdale. "Instead, we were able to implement some of the software's new rendering techniques to achieve the results National Geographic was looking for."
|Orbital and weather information and textures for the digital solar system, including that for the Earth and moon (top) and for Saturn and its moon Enceladus (bottom), came from NASA sources and is physically accurate.|
The design team developed two sets of images: a lower resolution version to enable acceptable interaction rates for users with slow Internet access and a higher resolution version for those with faster modems. "The less-detailed images are small and tend to pixelate when you move extremely close to a planet, but they provide an idea of the surface tex ture. With the high-qual ity images, even when you zoom close in to the planets, you see a smooth, detailed surface," says Grimsdale.
To minimize download bottlenecks, the application relies on streamed image data from the Web site rather than preloaded data. "We decided the most efficient approach was to download the bare 3D world, with drab, gray planets, then stream in textures. So when a user zooms in close, the detailed texture for that planet is streamed in," says Grimsdale.
While Superscape was modeling the 3D world, the on-line media team at National Geographic was putting together the HTML page in which the virtual model would be enveloped. The HTML page includes the pertinent planetary information, including the year a given planet was discovered, its mass density, and significant scientific features. The two teams worked closely to link the HTML interface to the 3D world. "We developed a fairly standard interface where you can click on the HTML text to jump into the virtual world, and from the 3D model you can easily bring up the HTML referring tool to learn more about the planet," says Grimsdale.
|Clicking on the 3D model of Jupiter leads to an HTML link providing information about the planet.|
The interactive solar system is currently running on the National Geographic Web site (www.nationalgeographic.com). Grimsdale is satisfied that the final product meets the magazine's primary objective of educating its readers about the solar system in an entertaining manner. "It's all well and good to present flat, 2D pages full of planetary statistics, but that's not very compelling," Grimsdale says. "With this 3D environment, people can jump from planet to planet to get a sense of their surfaces and look at asteroids and such. And getting caught up in the 3D experience encourages people to then sample the 2D reference data and actually pay attention to what they're seeing and reading." Ket Tools Superscape VRT
, Superscape (www.superscape.com