January 16, 2008
Stanford computer scientist makes splash with Academy Award for fluid simulation
The rushing floodwaters in Evan Almighty, the heaving seas of the latter two Pirates of the Caribbean movies and the dragon's flaming breath in Harry Potter and the Goblet of Fire all featured computer-generated fluids in spectacular action. The science behind those splashy thrills will be recognized Feb. 9 with an Academy Award for Ron Fedkiw, associate professor of computer science at Stanford, and two collaborators at the special effects firm Industrial Light and Magic (ILM).
"The primary work started a few years ago when we developed a system designed for the female liquid terminator in Terminator 3," Fedkiw said. "Almost immediately after that it was used in the first Pirates of the Caribbean movie to simulate the wine that the pirate skeleton was drinking out of the bottle in the moonlight. Things like the sinking ship in Poseidon and the large water whirlpool in Pirates of the Caribbean 3 are good examples of the system in action."
The system, co-developed with ILM scientists Nick Rasmussen and Frank Losasso Petterson (a former doctoral student of Fedkiw's), uses a method of simulating low-viscosity fluids such as water and fire, as in the explosions in Star Wars: Revenge of the Sith.
Contributing to a Star Wars movie was a particular honor for Fedkiw.
"George Lucas made Star Wars and, well, that changed the world for a lot of us," he said. "It's amazing what a movie can do to a civilization. I can only be grateful that he made three more of them and that I started working with ILM just in time to get a screen credit on the last one."
Computer graphics experts typically have used particles and complex blobs to represent water, but these can give rise to unrealistically lumpy or grainy surfaces. Alternatively, they have used a technique called "the level set method" that gives a smooth surface representation, but some water is "under-resolved" and simply disappears when it breaks down into small volumes, as in a crashing wave.
The key innovation behind Fedkiw and former doctoral student Douglas Enright's novel "particle level set method" was to mix the use of particles and level sets so that studios could maintain smooth surfaces wherever possible and still keep all the fluid via the particle representation.
"As an added bonus, the method automatically generates spray particles and bubbles in under-resolved regions where the level set [method] loses mass and volume," Fedkiw said.
Fedkiw gives a lot of the credit to his colleagues for the system used to make the movies: "Nick made the system and Frank made it rock."
The effect's power is clearly evident in a movie on Fedkiw's website. There, gigantic waves crash against a lighthouse and produce huge sprays. In addition to incorporating the particle level set method, the rendering also uses an additional method to simulate how the spray interacts with itself and the surrounding water.
Such integrations are indicative of a future direction of Fedkiw's computer graphics research.
"This year we built a system that allows two-way coupling between rigid and deformable bodies, so we can fully physically simulate bones moving around under fleshinteracting with the environment," he said. "Another main result is a two-way, solid-fluid coupling method that can be used with it, so the environment can be water; that is, we're going to be simulating people swimming."
Of course the more immediate future calls for a trip to the Beverly Wilshire Hotel in Beverly Hills for the Scientific and Technical Academy Awards presentation Feb. 9. Fedkiw says he'll probably go to pick up his plaque.
"After wearing sandals for the last two yearseven in the Lake Tahoe snow it's going to be tough to go black tie," he said.
David Orenstein is the communications and public relations manager at the Stanford School of Engineering.
A video referenced in the text below can be downloaded directly from this link, http://physbam.stanford.edu/~fedkiw/animations/lighthouse.avi. It requires the Divx codec available at http://www.divx.com.