Layer by Layer
Issue: Volume: 26 Issue: 4 (April 2003)

Layer by Layer

By Audrey Doyle

Usually, realism is the overriding goal of artists creating digital effects sequences for live-action films. For some projects, however, it doesn't make sense to strive for realism when the result will be visually uninteresting. In such situations, artists must achieve a delicate balance between what's realistic and what's engaging to make the shots work.

Such was the case for the effects artists at CIS Hollywood who worked on Paramount Pictures' The Core. In the live-action film, geophysicist Dr. Josh Keyes (Aaron Eckhart) discovers that an unknown force has made the earth's inner core stop rotating, causing the planet's magnetic field and atmosphere to deteriorate. To resolve the crisis, Keyes and a team of scientists journey down through the layers of the planet's interior in a subterranean craft piloted by "terranauts" (Hilary Swank, Bruce Greenwood) to detonate a device that will reactivate the core. CIS was responsible for creating the approximately 50-shot digital sequence in which the CG craft, dubbed Virgil, plows through earth's crust, mantle, and outer core, then sets off the explosion, travels back up, layer by layer from the center of the earth, and emerges from the ocean floor.

According to Bryan Hirota, CIS visual effects supervisor, the greatest challenge of this sequence involved making it look real, despite the fact that in reality it would be impossible to see any type of craft pushing through rock, lava, silicate compounds, and other elements. "If you were to try and show what a craft like Virgil would look like cutting through the earth's layers, you'd end up with a sequence showing lots of rock, lava, debris, and gases flying around, but not much else," Hirota says.

To accomplish the sequence, the team first turned to tools that would enable them to create scientifically accurate effects. "We based the animation—of the rock in the crust, the lava in the mantle, and what we call the hyperfluid, which is the super-compressed, super-hot solution of liquid and gas in the outer core—on physics and computational fluid dynamics," Hirota says. "We then took liberties in terms of visually telling a story that under normal circumstances can't be told, and of presenting it in a way that would be easily understood by audiences."

A team of about two dozen CIS artists and compositors had approximately eight months to complete the sequence. A portion of the work involved designing and building Virgil, the 150-foot-long, cigar-shaped craft that pulverizes everything it comes into contact with as it descends toward the core. To create and texture the model, artists used Alias|Wavefront's Maya and Interactive Effects' Amazon Paint. For rendering, they used Entropy, a RenderMan-compliant renderer developed by Exluna. (Exluna recently merged with Nvidia and no longer markets Entropy or its other flagship product, Blue Moon Rendering Tools, but is continuing to support existing customers.)

To simulate a journey through earth's inner layers, digital artists at CIS.Hollywood created solid rock, molten lava, and a host of volumetric and particle effects. Image © 2003 Paramount Pictures.

When creating underground scenes, artists were challenged to provide perspective where in reality there would be none. Image © 2003 Paramount Pictures.

The team spent most of its time creating the different layers of earth and animating the craft smashing through them. First, as Virgil pushes through earth's crust, it is surrounded by a plethora of particles and volumetric effects that the team created in Jig, a standalone volumetric renderer from Steamboat Software. "When Virgil reaches the mantle," says Hirota, "viewers see many of the same basic elements in terms of particulate matter and effects animation. And they also see an abundance of volumetric fluid effects simulating the magma in the mantle, which moves around Virgil with the consistency of honey."

Meanwhile, to animate the magma's movement as it comes in contact with Virgil, the team used Flow Analysis, a computational fluid dynamics solver from Flow Analysis. "Their product has been used for military aviation purposes—we worked with them to create a solver we could use on our Maya model," says Hirota

After passing through the mantle, Virgil reaches the outer core. Less viscous and particulate than the other layers, the outer core features Flow Analysis fluid dynamics effects moving around the craft. It also includes a luminous, "dynamic" atmosphere populated by millions of moving light particles created in Spore, a proprietary standalone particle system developed by Image Savant owner Richard "Doc" Baily and used to render the atmospheric effects in the film Solaris (see December 2002, pg. 21).

Finally, Virgil reaches earth's inner core, which is under such extreme pressure that it remains solid. The artists created the inner core using Entropy.

As a final step, CIS used Apple's Shake to composite all the shots except for those depicting the outer core, which were done in Discreet's inferno. Modeling, animation, and compositing were performed on Linux machines from Boxx Technologies and Angstrom Microsystems; rendering was done on Intel- and AMD-based Linux machines from Linux Networx.

According to Hirota, the most difficult aspect of CIS's work on The Core was achieving the right simulations from the fluid dynamics solver. "Any kind of dynamics simulation is prone to instabilities. It's unlikely you'll get a clean simulation that you're 100 percent happy with on your first try," he says. "A lot of our work involved running enough simulations, and coming up with ways to combine simulations, to achieve a pleasing result. In the end," Hirota says, "the results speak for themselves. This was the film's climax, and we wanted to set a high aesthetic bar."

Audrey Doyle is a freelance writer based in Boston.

Angstrom Microsystems
Apple Computer
Boxx Technologies
Discreet www.discreet
Flow Analysis
Image Savant
Interactive Effects
Linux Networx
Steamboat Software