Researchers at Purdue University are creating interactive software that artists could use to make realistic animations of cloud formations, explosions, smoke, steam, fog and other gaseous phenomena for movies and video games.

The same software might also be used by meteorologists to create accurate representations of quickly developing weather conditions. Because the software is interactive, it shows results immediately, whereas conventional programs might take hours to complete such animations, said David Ebert, an associate professor in Purdue's School of Electrical and Computer Engineering.

Joshua Schpok, one of Ebert's students, has used mathematical algorithms to design the software, which provides natural, intuitive controls.

"So an artist wouldn't have to deal with scientific details - such as pressure and density, thermal convection, the percentage of dust and ice particles and all of these things that a meteorologist would look at - we have created a control system that an artist can actually manipulate," said Ebert, director of the Purdue University Rendering and Perceptualization Lab.

Behind the scenes, complex mathematical algorithms compute parameters needed to simulate such behavior as developing storm clouds and the effects of wind on clouds.

Although the software, which Schpok has named Swell, specifically produces animations of cloud formations, the same approach also could be used to design software for animations of any gaseous phenomena, Ebert said.

Findings about the research are detailed in a paper to be presented July 26 during the Symposium on Computer Animation in San Diego.

The amorphous nature of clouds makes them more difficult to animate than figures of people or objects. Another complicating factor is that to be realistic, the semitransparent animations must show the interior of a cloud, not just its general shape, Ebert said.

"You can sort of see through parts of the cloud and see the inside, which is useful if you want to, say, move a camera through a cloud or manipulate it rather than just look at its surface," Ebert said. "With most movie special effects, like the computer-generated female in 'Terminator 3,' it's an opaque object.

"Most things in computer games and computer graphics are done as hollow objects represented by approximations of a surface. With a cloud or other natural phenomena, like water or fog, you can see through the entirety of it, so you need to have the full interior detail, which is much more complex for modeling and image generation."

The animation software could soon be applied to commercial uses.

"I think it would make an excellent plug-in to some of the existing modelers," Ebert said. "They have systems to grow clouds now that do a pretty good job, but the problem is that it takes a few hours for the systems to produce the animation.

"If you are doing an animation, you tend to have to come back the next day to see what the actual sequence looks like. But with our system, you are interacting with the animation in real time, controlling it and changing how it evolves over time so you immediately see it and know what the results are.

"The fact that this is interactive means you could use it in video games, which now have very limited cloud-type effects."

The research was funded by the National Science Foundation and the U.S. Department of Energy.

The symposium in San Diego was organized by the Association for Computing Machinery's Special Interest Group on Computer Graphics and Interactive Techniques, and the European Association for Computer Animation. The research paper was written by Schpok, Ebert, Charles Hansen, an associate professor of computer science at the University of Utah, and Joseph Simons, an undergraduate student in computer science at Purdue.

Schpok began working on the system about a year ago. The 22-year-old student from South Bend, Ind., recently graduated with two bachelor's degrees, one each in mathematics and computer science. He will begin graduate studies next fall in Purdue's School of Electrical and Computer Engineering and plans to improve the visualization software.

"I am continuing to expand it in different directions," Schpok said.

Purdue engineers want to increase the types of lighting reproduced in the animations. Examples include the effects of light from a setting sun and the "bluing" of clouds caused by the atmospheric scattering of light.

Purdue University engineering student Joshua Schpok has created a software program, called Swell, that can be used by artists to create realistic animations of cloud formations for movies and video games. The same approach also could be used to design software for creating animations of any gaseous phenomena, such as explosions, smoke, steam and fog. This image is an example of a cloud from one of the animations. (Purdue University graphic/Joshua Schpok)

ABSTRACT

A Real-Time Cloud Modeling, Rendering, and Animation System

Joshua Schpok, Joseph Simons, David S. Ebert, and Charles Hansen

Modeling and animating complex volumetric natural phenomena, such as clouds, is a difficult task. Most systems are difficult to use, require adjustment of numerous, complex parameters, and are non-interactive. Therefore, we have developed an intuitive, interactive system to artistically model, animate, and render visually convincing volumetric clouds using modern consumer graphics hardware. Our natural, high-level interface models volumetric clouds through the use of qualitative cloud attributes. The animation of the implicit skeletal structures and independent transformation of octaves of noise emulate various environmental conditions. The resulting interactive design, rendering, and animation system produces perceptually convincing volumetric cloud models that can be used in interactive systems or exported for higher quality offline rendering.