Issue: Volume: 24 Issue: 8 (August 2001)

Raptor Redux

By Barbara Robertson

© 2001 Universal Pictures. Photo credit ILM.

When the crew at Industrial Light & Magic (San Rafael, CA) was asked to recreate the dinosaurs from Jurassic Park for the third time, they did what any effects crew would try to do: produce something more incredible than last time . . . or the time before.

"Everybody who got on this show realized the movie had been done twice before," says Jim Mitchell, visual effects supervisor for Jurassic Park III. "It was our chance to show we could make something new and exciting."

In the Universal Pictures film, directed by Joe Johnston and released July 18, moviegoers once again watch prehistoric dinosaurs terrorize a few intrepid visitors to Isla Sorna, the original Jurassic Park location. To help enliven the sequel, ILM developed new techniques for the visual effects in two main areas: The team created a simulator that moves the digital dinosaurs' skin across muscles and bones in a realistic manner, and they made breakthroughs in integrating the dinosaurs with the environment.
In this film, the CG dinosaurs interact more closely with animatronics and with the environment than in earlier Jurassic Park films. Here, the raptor on the left is an animatronic and the two on the right are digital.

"It's not enough just to do the dinosaurs," says Mitchell. "Now the big thing is what you do to make the dinosaurs part of the scene."

To help the dinosaurs look like they be longed in the environment, the effects team focused on two issues: matching the CG dinosaurs to the animatronics, and creating photorealistic natural elements-including, for one dramatic sequence, an entirely CG world.

Unlike the earlier movies in which the camera would cut from animatronic to CG dinosaurs, in Jurassic Park III, both types of dinosaurs appear in the same scenes, sometimes nose to nose. For example, during a fight between a spinosaurus and a T rex, sometimes the T rex is CG, sometimes animatronic; sometimes the spino is CG and sometimes animatronic. It's im possible to tell which is what, even in close-ups. In another scene, CG and animatronic raptors surround actor Sam Neill. "It's amazing to be on the ground, right in front of a 12-ton creature and see it power up," says Mitchell of the animatronic. "It puts you into the moment."

To create CG dinos that looked as real, ILM's painters used photographs of the animatronics as reference for painted texture maps, and created displacement maps so the renderer would carve surface geometry into a lizard-like texture.
A script-based tool that layered a soft-body muscle simulation over the performance animation was used to move the dinosaurs' muscles; a volumetric simulation system also developed at ILM used a point mesh to move skin over the bones and muscles.

The effects team got a surprise, though, when they looked at the first live-action plates. In reference photos, the animatronics were brownish, but lights on the set had given them a bluish cast. Moreover, colored filters had created patterns in hues of green, orange, and blue that slid across the animatronics' skin as they moved in the live-action plates, to give the impression of a canopy of jungle foliage. "We had to match the same color space," says Samir Hoon, sequence supervisor. "So, we ended up using ambient occlusion."

This rendering technique, developed at ILM for Pearl Harbor (see "War Effort," June 2001, pg. 22) to simulate diffuse light in an environment, added colors from the plate to the rendering of the dinosaurs' skin. To make ambient occlusion useful for Jurassic Park III, the team had to extend the technique so that it worked with deformable, animated creatures and would handle motion blur and displacement-effects not needed in Pearl Harbor. The ambient occlusion technique worked so well it was used for all the sequences. Sometimes, ambient occlusion and reflection maps provided all the light needed for a scene.

For example, in one scene the wet body of a spino walking through a lake reflects a fire burning in the foreground. "We would run the reflection map and the ambient map on every frame from the plate and get the flickering lights and flames on the spino automatically," says Christophe Hery, CG supervisor. "It was a major breakthrough."

"The ambient technique is not the only technique you want to use, but it's a great help," he adds. "It freed the technical directors so they could focus on adding key lights and secondary lights to make the creatures look beautiful instead of spending time placing fill lights." All the CG creatures and scenes in Jurassic Park III were rendered through Pixar Animation Studio's Render Man, with Mental Images' Mental Ray helping with the ambient occlusion.

Fitting the dinosaurs into the environment also meant helping the beasts look as if they were interacting with the environment. When a dinosaur crashes through the forest, it moves trees and plants aside, tramples grass underfoot and splashes water when its big foot steps in a puddle. In the first Jurassic Park films, people on location or on the set moved trees and plants with rigs, and painters removed the rigs from the plates later. Thus, animators had to position their digital dinosaurs so that it looked like the animals were interacting with the trees and plants in the plate. This time, though, the animators created the performances they wanted and the technical team fixed the plate to match.

In the sequence with the two dinosaurs fighting, for example, dozens of CG elements added after the dinosaurs were animated helped make the live-action environment livelier. The effects team put a puddle under a dino's foot, added little animals that scurried away from the frightening beasts, showered the thrashing dinos with falling leaves, and added plants. "We've reached a point where the plate is almost secondary to us," says Hery.
To intermingle the dinosaurs with the environment, ILM added CG plants created with Maya Paint Effects to the live-action plate and used ambient occlusion to add colors from the plate to the dinosaurs' skin.

Throughout the film, the dinosaurs brush aside vines that exist only in the computer and move plants that are half digital and half real. "We were really plant happy in this movie," says Hoon. In one shot, for example, all the ferns in the live-action plate were replaced with CG ferns so the plants would move automatically when a CG raptor ran through them.

To create plants, the team used Alias|Wavefront's Maya Paint Effects running on SGI workstations. "Paint Effects doesn't motion blur properly, so we had to come up with solutions for that," Hery says. "But it's quick. You just draw brush strokes and grow leaves out of that."

Rather than use the dynamic engine in Paint Effects to animate plants, the team developed a separate system based on particle dynamics "When any part of the raptor touched a plant, it would respond correctly," Hoon says.

Here's how it worked: First, they drew a plant in Paint Effects and separately, a curve (a spline) the same height and then attached the two. Next, they converted the spline into a soft body, turning each point on the spline into a particle so that it would respond to collisions using typical particle dynamics. Thus, when a particle collided with a piece of geometry, it moved; and when a particle moved, the Paint Effects plant followed.

To render the plants, the team borrowed an idea from ILM's crowd pipeline. "We created libraries with instanced geometry for vines and leaves. Instead of instancing cycles of animated creatures, we instanced cycles of moving leaves," Hery says.

If it's possible to create plants photorealistic enough to live alongside plants filmed on location, why not create an entirely synthetic location? For much of the so-called aviary sequence, the team did exactly that. "I'm partial to this sequence because it's so fast paced," says Mitchell. "You're flying alongside pteranodons."

The 15-minute sequence takes place in a 100-acre, fog-enshrouded canyon with steep, craggy, 300-foot walls, down which waterfalls cascade into a rapidly flowing river. It's the pteranodons' aviary and nesting ground, and much of the 15-minute sequence was created entirely with computer graphics.

At one point during the sequence, a pteranodon walks out of the fog, plucks the child, Eric (actor Trevor Morgan), off a bridge across the canyon, and flies with him dangling from its talons to a nest of hungry fledgling pteranodons.

The actor was filmed on a bluescreen stage hanging from bird-like legs, which were moved on a rig. To give animators freedom to move the bluescreen boy in 3D space, the effects team attached a "card," (a polygon), to the CG pteranodon's feet. Then they mapped the bluescreen character onto the card. The rest of the environment was created with Avid's Soft Image 3D models and RenderMan shaders.

The shaders do most of the work. In fact, a view of the undressed geometry looks like a bad virtual reality scene. The nest sits on tall, garishly colored cylinders, the walls look like flat planes, the boy in an egg-shaped slice of bluescreen hovers above the animatronic nestlings, and it's hard to believe this will become a photorealistic landscape.

The shader, masterminded by technical director Toan-Vinh Lee, turned the canyon walls into rocks, created waterfalls and a river below, and grew ferns and foliage on the walls. Fractal-based displacement created the crevices and rock formations. Plants were grown in the walls based on proximity fields. "You paint a map that pinpoints where you want the plants to be grown," says Robert Weaver, sequence supervisor. Specular noise created the waterfall and a canopy with a grid pattern was formed from simple patches, all in RenderMan.

To create a dense fog that matched what the fog machine generated on stage, Hery opted to work with spheres in Soft Image to position the fog in 3D space. He then rendered the spheres with simple RenderMan shaders that used fractal noise-a faster process than if he'd used particle or volume simulation.
In these images, nearly everything except the actors is digital. The scenes in this 15-minute sequence take place in the pteranodon's aviary, which is in a domed, 100-acre canyon with craggy, 300-foot walls. The rocks, water, plants, catwalk rigging,

In addition to the foggy canyon, the sequence also had CG water created with a combination of a fractal-based shader and particle mist, a completely computer generated parasail, a sort of parachute-like flying ma chine developed by technical director Nigel Sumner, and many flying CG pteranodons.

The film, of course, had a host of other prehistoric digital animals ranging in size from two-feet to 51-feet tall, all modeled in Alias|Wavefront's Power Animator and ILM's ISculpt. In addition to velociraptors, spinosauruses, T rexes and pteranodons, the film also starred CG brachiosauruses, ankylosauruses, compsognathuses, parasaurolophuses, corythosauruses, stegosauruses, triceratops, and ceratsauruses.

Making all these dinosaurs move realistically took the efforts of the animation team, led by Dan Taylor, but the skin simulations created by the technical teams helped. Sebastian Marino, CG software developer, based the new skin simulation techniques on volumetric simulations developed by John Anderson, CG scientist, that were first used for The Mummy.

"Basically what we simulate is the volume of the skin and essentially the fat layer of the creature," says Marino. A three-dimensional point mesh, in which any vertex could connect to any number of other vertices, created the simulation.

This "flesh mesh" has the characteristics of foam and Jell-O. Like foam, when one end of the mesh is squeezed, it compresses but the other end doesn't get larger, and when the pressure is released, the mesh returns to its original shape. And like Jell-O, it jiggles.

To create the simulation, a dinosaur's volumes-its torso, arms, legs, and tail-were filled with the mesh, and the mesh was linked to the creature's primary motion. "It's as if the mesh is attached to a centerline down the volumes of the creatures," says Tim McLaughlin, creature supervisor. "As the critter moves, the mesh goes along for the ride."

The amount the mesh moved and jiggled during that ride depended on various stiffness and damping parameters and on whether there were obstacles such as muscles or bones in its path. The mesh contoured over muscles and bones that pushed it from one place to another as they moved-imagine punching a foam pillow. Also, waves of motion propagated through the mesh-imagine shaking a bowl of Jell-O.

Thus, the simulator caused the belly of the T rex to shake like Jell-O; and, at the other end of the spectrum, caused muscles to ripple under the skin of the raptors' athletic bodies. "As the mesh gets pushed from one place to another, you can see what's driving a creature, which is something you never get with enveloping," Marino says. "First, you see muscles flexing, and then the leg goes forward and extends. As the creature steps down, you see the muscles tighten up and see that movement affecting the fat layer."
To integrate digital raptors in this shot, ILM added digital smoke to practical smoke, created digital vines, replaced the plant on the right with a CG plant that would move, added dust elements, and rendered the dinosaurs with ambient occlusion.

The skin sims were not used for every shot-motion blur and camera shake, for example, would often hide the effect. When they were used, however, the team discovered the simulator had a positive effect on textures: It prevented texture stretching. Because it stretched the skin globally rather than locally, the skin moved more naturally. "The simulations didn't alter the way the models were painted, but the textures looked better when the dinosaurs moved," says McLaughlin.

All told, ILM created 406 shots for the film, nearly eight times the 55 visual effects shots created by the studio for the first Jurassic Park. That movie convinced Hollywood that movies with computer graphics creatures could be both cost-effective and box-office hits. "We were breaking ground then, putting detail into reptilian skin textures, creating realistic animation, faking how skin reacts to the way bones move," says Mitchell, who was a technical director for the original Jurassic Park.

Eight years later they've done it again. ILM improved on the original breakthroughs and pushed the state of the art further with the skin simulations and by intermingling CG dinosaurs with animatronics. Moreover, while the first Jurassic Park demonstrated that CG dinosaurs made production sense, this one shows that totally synthetic natural environments do, too. "You can always make an environment that's stylized," says Weaver. "But if you're trying to sell it as photoreal, you've entered a new ball game. To be able to do that within a budget that's feasible from a production standpoint is really important."

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