Issue: Volume: 23 Issue: 4 (April 2000)

MISSION POSSIBLE




by Barbara Robertson

Filmed in a style more reminiscent of 2001: A Space Odyssey than a Star Wars movie, Touchstone Pic tures' Mission to Mars rolled into US theaters March 10, becoming the first in a predicted spate of Mars-related stories this year. Early reviews were mixed: Some critics loved the style; others found it boring. Directed by Brian dePalma, recently of Mission Impossible fame, it's a science-fiction adventure set in the not-too-distant future that offers visual-effects aficionados fantastic storms on Mars created with fluid-flow simulators and particle systems, numerous scenes with apparently weightless astronauts, and some interesting holographic projections created with 3D computer graphics.

Two California studios, The Secret Lab (TSL, formerly Dream Quest Images) now in Burbank and Industrial Light & Magic (ILM) in San Rafael, created the bulk of the visual effects, with Tippett Studios in Berkeley also contributing a few shots. TSL started the project alone; the other studios were brought in when the release date moved forward and the number of effects shots increased, according to Hoyt Yeatman, visual effects supervisor at TSL.
The effects crew at ILM created the CG cable, assembled the Mars surface by tiling Viking images, and composited those elements with blue-screen film of the astronaut.




The first five minutes of the movie are on Earth. After that, everything happens onboard spaceships, in space, and on the surface of Mars. Before the effects teams began creating these artificial environments, Yeatman created CG animatics or 3D storyboards using Alias|Wavefront's (Toronto, Canada) Maya software. "We built whole sequences in 3D in Maya that were edited by the film's editor, Paul Hirsh," he says. The 3D animatics also provided data for building sets and positioning equipment. Once the physical elements were in place, they were surveyed, and the survey data was fed back into Maya to fine-tune the virtual elements and create accurate virtual sets.

Some of these virtual sets included exact models of the huge motion control camera rigs and rigs for the "weightless" actors as well as virtual replicas of miniatures and live-action sets. "Brian [de Palma] does what I call 'cosmic zooms'-big, unusually designed, con tinuous shots," Yeatman says. "We were able to plot them in the virtual environment and use the data to drive the motion-control cameras." This reduced the need for tedious and time-consuming motion tracking. "The [live action and CG elements] hooked up exactly," says Darin Hollings, TSL digital effects supervisor.
The particle-system explosion, the star fields, the orbiting planets, and the room are all visual effects created at ILM.




TSL's most challenging CG element, according to Hollings, was the "vortex." To set the scene: As astronauts on the first manned mission to Mars get close to the planet, they see a shape that could be a mountain formed by water. When they're on the surface, they use radar to determine the supposed mountain's composition. This action inadvertently triggers a whirlwind that blows rocks and debris off the "mountain," revealing a huge structure shaped like a face. The resulting sandstorm evolves into an inverted tornado-the vortex. One astronaut spins into the vortex and disappears. Another falls on the ground. A third is chased by the vortex and is sucked inside where he explodes.

To create the vortex, TSL used a proprietary fluid-dynamic simulator that can render hundreds of millions of particles, according to Hollings. Called "Hookah," the software was originally developed for the movie Armageddon to create a gaseous cloud. For Mission to Mars, the simulator was modified to create the more particulate vortex and to give the director control of the movement. To help channel the vortex simulation, the effects team created a series of nested cylinders in Maya. Dynamic forces in the outside cylinders try to push particles toward the inside, and forces in the inside cylinders try to push particles out. Animators used inverse kinematics and keyframe animation to position the cylinders, and thus the vortex over time.

To insert spinning rocks and astronauts inside the giant vortex, the effects team used information from the virtual set to create Z-depth maps of these elements. The maps were used as holdout masks to create holes in the rendered vortex where the compositors could later insert elements at various depths. To further create the illusion of depth, dust particles were rendered with various degrees of opacity determined by their distance from the camera. TSL used six SGI (Mountain View, CA) Origins with 16 processors and 16gb to 24gb of RAM to create and render the vortex. There were 36 vortex scenes ranging in length from 100 to 600 frames; a mistake in one frame meant re-running the entire simulation. "Some scenes took weeks," Hol lings says, remembering one that was particularly challenging, a 450-frame scene during which the (virtual) camera moves through layers of particles to reveal an astronaut's face as he's be ing blown apart.
To illustrate the evolution of life on Earth in a holographic display, ILM created this animation of animals evolving from paramecia to modern man using an innovative new 3D morphing technique. (continued in next image below)




Because there might be survivors from the first mission, a rescue team is sent to Mars, and we follow these astronauts through the rest of the film, which includes scenes created at ILM with astronauts outside the spaceship, inside the face, and leaving Mars. "Ori ginally, we were given 30 to 40 shots inside the face, but that scene got longer and our work expanded to between 300 and 400 shots," says John Knoll, visual effects supervisor at ILM. "We got cut [edited] sequences in November, and delivered shots in mid-February. The number of shots per week was higher than on Star Wars."




On the way to Mars, micrometeoroids hitting the rescue ship cause the engine to explode. The astronauts must evacuate. For tunately, a re-supply module is close. An astronaut jets toward the module with a cable in hand. He hooks the cable, but misses his landing and drifts off. The remaining astronauts safely follow the tether to the second ship. This scene was shot with the actors in astronaut suits against blue-screen or black. Everything else is CG-the looming surface of Mars below, the cables, the star fields, and in all but the very close-ups, the ship.
The Secret Lab animated this vortex by using force fields in Maya to help control the millions of particles generated and rendered with "Hookah," TSL's proprietary fluid simulation software.




"The actors wore wire rigs, but there was so little movement, they could have been on apple boxes," says Pat Myers, CG Super visor. To give them a weightless feel, the effects team created a 3D simulation in Maya that showed the spatial relationship between astronauts moving in zero gravity. Then, using ILM's Sabre system, a compositing system built around Discreet's (Montreal, Canada) Flame, they created 2D transformations that moved the filmed astronauts to match. The simulations also helped the team position the CG cable and insert particles for jets and thrusters. For the surface of Mars, they used actual, high-resolution Mars imagery. They even added CG dirt and other surface textures to the physical ship model used in the close-ups. "It looked so smooth, we knew people would think it was a CG model," laughs George Murphy, co-visual effects supervisor at ILM.

When the astronauts land on Mars, they meet the sole survivor of the first mission, who discovers how to go inside the hollow face. Once inside, they find them selves in a holographic display that reveals the origin of life on Earth. Everything inside the face except the astronauts is a CG element created at ILM. "We used RenderMan shaders to create star fields and NASA photo graphs on rendered spheres for planets," says Myers. The surface texture for the holographic Martian woman was created with a "complicated RenderMan shader;" a particle system transformed Mars from a green planet to a red one.




The Martians Will Be Us * Most impressive, however, is the 1951-frame, 81-second holographic evolution sequence. It begins with what looks like a microscopic slide of swimming paramecia. These evolve into fish, which morph into lizards, to walking crocodiles, dinosaurs, hairy mammoths, buffalo, to men running with torches beside the buffalo. Finally, the camera pulls up to look down on city lights at night. New extensions to ILM's animation software CARI smoothed the transitions between the animated animals. Christophe Hery, CG supervisor, explains that first they created models for the seven creatures, each with its own textures, shaders, and enveloping. From these, the animators could create finely tuned 3D morphs as the creatures walked. "In a given frame, you might see a blended creature whose arm is 80% buffalo, 10% mammoth, and 10% crocodile," Hery says. "Each cv [control vertices] on a creature can receive a different morphing value." The entire sequence includes hundreds of CG elements in addition to the evolving creatures-dust, glowing torches, shafts of light and particles in the water, and a complex terrain with animated grass.

In addition to the new morphing software, Hery's team worked with two other new pieces of software. One program was used to break a patch model into fragments with textures. The second is a new simulation-based engine designed by John Anderson to create a vortex with millions of particles that would evoke TSL's vortex. Unlike the earlier vortex, this one needed to be fiery rather than particulate. "We started with a volume renderer, but there wasn't time," says Hery. "So instead, we rendered lots of particle passes." Essentially, compositors would put the particle pass layers together using big particles as gaseous fluids around smaller particles.

"We had to figure out some new things, and there was a large volume of work with some deadline challenges, but it wasn't horrifically difficult," Knoll says. "Star Wars was great practice."

Barbara Robertson is Senior Editor, West Coast, for Computer Graphics World.
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