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Reader SurveyWater, Water Everywhere
Mar 1, 2008 12:00 PM, By Ellen Wolff
The Sci-Tech Awards honor believable sims.
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Accurately simulating the quick motions of water is difficult, covering a gamut of techniques—from the simulation of gross wave motion through secondary simulations of spray and mist.
Directing Waves
While the science of fluid simulation may be clearer, the art of using it for movies is getting more complex. Director Gore Verbinski wanted the water in Pirates 3 to look realistic, but also do impossible things to serve the story.
“The term is ‘directability,’” says Ray Feeney, longtime member of the Academy's Sci-Tech committee. “You start with reality and then warp it to the director's vision.”
ILM's Rasmussen knows that challenge well. “You do water that's physically correct, but the director wants it deeper, or choppier. The challenge has been to do something plausible to the eye that obeys the laws of physics, but now we have to direct fluids to get the effect a director wants without overcontrolling it and making the physics go away.”
“You need a solid foundation of water that's physically correct, but that's just the starting point,” says Digital Domain (DD) honoree Ryo Sakaguchi, who worked on fluid sims in Pirates 3 and The Day After Tomorrow. “We then have to fight artistic controllability.”
Simulations that serve both the imagination of the audience and the vision of the director, were created by deserving recipients of technical honors at this year’s Sci-Tech Awards, such as Rhythm & Hues’ Michael Kowalski, Jeroen Molemaker, Jonathan Cohen, and Jerry Tessendorf (pictured, left to right).
“Everyone wants bigger, faster, and better simulations. But bigger sims get slower, and artistic control is all about doing more iterations,” Roble says. “Then there's that word ‘better.’ One of the big problems in fluid simulation is that it's easy to make a fluid simulator that simulates oil, but accurately simulating the quick motions of water is difficult. That's what we're all working on.”
“The trickiest part is the fine detail,” Tessendorf says. “It doesn't do any good to do a sim at low resolution and then try to build it up in stages. The whole process of adding details onto an existing simulation is an artistic demand that you can't meet by cranking up a number.” R&H uses a collection of software, including the AHAB sim tool and a scripting language for dealing with volumetric data called Fueled Expression Language Toolkit (FELT). “We can do brute-force simulations without a lot of detail, and we can then apply that in the scripting language to generate finer motion without much computational difficulty. You have to cheat the physics to make it work artistically,” Tessendorf says.
Animating believable fluids is one problem, and rendering it to look real is another. Today's sim systems feed directly into renderers. ILM's sim software operates within the studio's proprietary system Zeno, and current efforts are being directed at enabling artists to handle complex interactions between water and objects such as ships. “Everything we build is to achieve an effect — and then do lots of it,” Rasmussen says.
While proprietary sim systems provide the power and flexibility to achieve custom solutions, several studios that haven't built their own tools are still tackling fluid sims by purchasing Real Flow from Madrid-based Next Limit Technologies. Honored with a Technical Achievement Award, Real Flow has been used by Blue Sky Studios for Ice Age: The Meltdown, Asylum for National Treasure: Book of Secrets, and WETA Digital for The Lord of the Rings: The Return of the King. “Most of our customers come from the movie industry, so we've created a product for artistic use,” says Victor Gonzalez, who shares Next Limit's award with Ignacio Vargas and Angel Tena. “Artists don't want to deal with the math.”
