Issue: Volume: 31 Issue: 1 (Jan. 2008)

Casting Crusoe


Despite its name, the “water horse” looks nothing at all like a horse. Implicit in its name, though, is one of the two challenges that Weta Digital faced in creating visual effects for the movie Water Horse. That challenge, of course, is water, and more exactly, integrating a CG creature into that water. The other is the creature itself.

The Columbia Pictures film, directed by Jay Russell, follows the relationship between Crusoe, the creature, and a young boy as the two stretch toward adulthood. When full grown, Crusoe resembles what people picture as the Loch Ness monster; that the story takes place in Scotland is no coincidence.

The story, which is set during World War II, stars Alex Etel as Angus MacMorrow, a lonely young boy. His father is a soldier who, we learn during the film, will not be coming home. As the fantasy adventure begins, Angus discovers an oddly shaped egg that soon hatches a sea creature, a water horse. The water horse is born an orphan; each creature creates one egg and then dies.

“Crusoe is one of the creatures the world is not supposed to know exists,” says Joe Letteri, senior visual effects supervisor at Weta Digital, where a crew that topped 200 worked on 600 visual effects shots. “We had this idea that he’s lonely, but also naïve and playful. We first see him when he hatches from the egg and he’s a baby bird: cute, but messy and ugly at the same time. He and the boy have to quickly find each other and bond.”


A new, layered approach to subsurface scattering gave Crusoe’s sea-creature skin extra fleshiness and warmth.

Crusoe: Newborn
Crusoe began his film career at Weta Workshop, where modelers created detailed maquettes of the first three “life” stages—infant, puppy, and teenage—and the head and neck for a full-sized, 22-foot creature. Weta Digital scanned early versions of the maquettes to animate 3D models of the puppets for previs.

“We did early scans to get an idea of how the character would work in 3D,” says Richard Frances-Moore, animation supervisor. “The look of his face was particularly important because he had to be expressive. Crusoe’s face is very three-dimensional. The sides look different from the front, like a dog’s face, so expressions that are modeled change significantly when you look at them from different angles.”

Crusoe doesn’t talk, but his expressions are recognizable, like those of a dog, which Weta Digital used as reference for the facial animation. “We didn’t want to humanize him,” says Letteri. “But, everyone can understand dog emotions.” Also like a dog, he makes noises. He barks, squeaks, and growls.

For his infant stage, the animators used newborn birds, baby turtles, and lizards as reference. “Jay [Russell] was specific that we needed to believe this was a newborn creature, so we focused on giving him shaky movement,” says Frances-Moore. “Because he didn’t have full control, he’d overshoot. We’d start his movement sharply, like an electrical impulse, and then have it dissipate and smooth out at the end as his weight took over.”

To render Crusoe’s skin, CG supervisor Martin Hill developed a new, layered approach for subsurface scattering, which was particularly important for the infant stage. “We wanted to see the veins through his skin and the fleshiness underneath,” says Chris White, visual effects supervisor. “Instead of having subsurface scattering just going through a skin layer, we added layers beneath.”

Maps created by texture painters defined a blood layer that shaders also controlled by adjusting the amount of visible skin or painted veins beneath, based on the viewing angle. “If you’re looking down at him, you can see more of the blood layer,” says White. “Crusoe was a perfect creature to test this on because he’s so small and had a baby-bird look. When we got good results, we used it for his puppy stage as well.”

Crusoe: Puppy
Because the two subsurface scattering layers had worked so well for the infant stage, the technical crew gave the puppy stage a third, fat layer. “It was a natural progression as we learned how the technique worked,” says White. “By lightening his muzzle and the area around his eyes, we added a level of cuteness and tied him back to the infant stage. He progressed so quickly; we wanted to make him feel like the same creature through all four stages.”


Weta Digital gave young Crusoe a puppyish charm using well-honed animation and rigging tools enhanced with a new flesh and muscle dynamics system.

For each stage of Crusoe’s life, the studio built and rigged a completely separate creature, even changing his face shapes somewhat. As Crusoe grew into his “puppy” stage, animators switched to references of seals and otters for his body movement. “The puppy and adult stages are the most important,” says Frances-Moore. “In his puppy stage, he’s the most fun: adventurous and slightly silly. At this stage, he really bonds with Angus, and the audience has to fall in love with him.”

The “puppy” Crusoe soon finds the bathtub, and his flippers became important on land and in the tub. “The flippers were quite tricky to rig,” says Frances-Moore. “They’re like a long, long hand with support on the very tip and at the ‘wrist.’ If you look at a seal’s flipper, it’s effectively full of fingers underneath, like a hand hidden within. We had to build an advanced reverse-IK rig to control the contact point anywhere along the hand.”

For facial animation, Weta Digital has developed an Autodesk Maya-based system that gives the animators blendshapes that understand the creature’s facial structure. Rather than simply blending from one shape to another, the system takes into account the underlying shape, whether flesh or bone, and reacts accordingly.

But, to give the young sea creature some baby fat and a seal-like quality, the crew developed a new system, called Pogo, to jiggle the fat. “The fat jiggle is defined by the tension of the surface,” explains White. “Animators could identify points on the surface and specify how much weight to apply in certain areas. They might give the loose skin under his neck a certain tension, for example. Or, the creature department might set up his belly to have a particular kind of movement.”

In addition to flesh dynamics, the system, developed by CG supervisor Simon Clutterbuck, also managed muscle dynamics. “Some muscle movement comes through the IK, so when the animators are moving the chains, you get a natural muscle movement, but this system created the secondary movement,” says White.

On set, a blue puppet helped the actors have something to touch and look at, but in the digital world, the muscle deformation system helped Crusoe’s body react properly when someone touched him.

Crusoe: Teenager
One of the goals the team had for the teenage Crusoe, who appears in fewer shots, was to transfer the character’s personality and appearance to a suddenly cow-sized creature. “Just like a kid, the teenager is not comfortable around the house,” says Frances-Moore. “He quickly moves into the loch, [and that change] is a driving force for the story, but he’s still very much the same character. So, one of the things we did when he jumped to the larger size was to keep his puppy aspects alive, like a big dog that still has a puppy inside.” For reference in this stage, the animators looked at sea lions.

Texture maps and shaders helped Crusoe maintain consistency through his life stages. Like the puppy, the teenager has a slightly lighter snout and the same patterns on his skin. “Even as an adult, his texturing still holds true,” says White. “So does the expression in his eyes.”

To help with Crusoe’s eyes, the crew wrote shaders with new caustics. “Once we have the shaders working, it comes down to lighting,” says Letteri. “The lighting TDs always try to pop a little light in his eyes.”

Lighting TDs fine-tuned each shot to adjust the wetness and reflections. “We spent a good deal of time on lighting his eyes,” says White, “making sure his expressions are readable.”

Crusoe: Adult
As an adult, Crusoe spends all his time in Loch Ness and, therefore, the animators used whales and dolphins as reference for his body. For his face, they moved from dogs to horses. “His face is bonier and more structural,” says Frances-Moore. “He doesn’t have the flexibility of the puppy, but he has the same flow of expression.”

To help convince the audience that the adult Crusoe is the same creature as the puppy they loved, the animators employed a running gag. “He’s hungry all the time,” says Letteri. “It’s a great gag because it’s always getting him in trouble, and it allows us to push his growth. Angus feeds him from his infant stage to puppy. When he was hungry, he rubbed his nose against Angus, which was cute when he was a puppy. Then, when he’s a big, looming, majestic creature as an adult, and we don’t know if he’ll eat Angus at first, he puts his nose down and starts to nudge Angus in the same way. So, we get a moment of reconnection.”

In his earlier stages, Crusoe spends some time on land, but once an adult, he doesn’t leave the water. To help the large creature swim, animators developed new techniques. “It’s difficult to animate him in a pose-to-pose way,” notes Frances-Moore. “He’s so large and flowing, and all his parts work somewhat independently.”

Thus, to make it easier to change and edit Crusoe’s performance, animators could create a cycle for the creature swimming in place and then put it on a path, which caused the creature to flow through the path and achieve an underwater feel.


New water simulation tools could simultaneously produce detailed water movement around Crusoe’s body and low-resolution ripples farther away.

“Rather than moving the creature in world space, you could animate with reference to the spline that you push him along and make changes based on that,” explains Frances-Moore.

For scenes in which Angus rides on the back of the giant water horse, the crew constructed an enormous water tank—100x150x8 feet—and surrounded it with a 120-foot bluescreen. Alex Etel, the actor playing Angus, rode a blue jet-ski based rig in the big pool.

“It was trickier than we had anticipated,” says Erik Winquist, co-visual effects supervisor and compositing supervisor. “Crusoe is an organic, flexible creature with a lively performance, not like the fiberglass neck on the jet-ski rig. We had surprising cases where, because of extensive previs, the animation stayed true to what they shot, but in the nighttime race on a dark, stormy loch, the animation had to amp up. Once it deviated from the puppet neck, we had to patch and replace things.” Compositors pasted in bits of Angus’s arm and his face, and sometimes inserted a complete digital double.

Even trickier, of course, was the interaction of Crusoe and the water.

Moving Water
“This show was all about water, and that’s not an easy thing to deal with,” says Winquist. “It’s always moving. You can never lock anything onto it.”

The crew shot much of the movie in New Zealand, with two weeks of footage also filmed at Loch Ness in Scotland. “We used a lot of practical water,” says Letteri. “But, the water is always a combination of shot elements and digital water.”

In the bathtub, a gray puppet performed by a puppeteer on set created splashes for the puppyish Crusoe and provided lighting reference. Because the animators used footage of the puppet as a basis for Crusoe’s digital performance, the compositors were able to use the real splashes. “It was a blessing,” says Winquist.

Once Crusoe stepped into the loch, though, the water became more difficult. When Crusoe rises out of the water, it    slides off his back; when he swims, he creates a wake. “To have water sheet off his back, we originally tried using a filmed element of water sheeting on a large pane of glass as a 3D displacement,” Winquist explains. “But, we found the easiest thing to do was a UV render pass for Crusoe and use that to direct the flow of water, like wrapping paper around his neck.”

By mapping coordinates from the tip of the creature’s nose to the base of his tail, the artists wrapped the sheet of water around him like a cylinder and used red and blue channels to define the flow direction. The UV pass allowed compositors to dial in the amount of flow depending on how much water the director wanted to see.

“We shot the water at 24, 48, and 72 frames per second,” says Winquist. “For close-up shots, we used the slower water to give us more scale.”

The jet-ski shot was particularly difficult. “We had to put two plates together, the lake plate and the shot of a blue sled through the water,” says Letteri. “That meant replacing some water in both plates with digital water and then shooting 2D elements to stitch it back together again.”
   
Water Interaction
Indeed, although the crew used puppets and other devices on set to get true water dynamics, digital water often supplemented the live-action elements, especially when Crusoe interacted with water in the loch. For this, Chris Horvath developed a new water solver based on particle-level sets.

“Chris made some advances so we could do close simulations and also affect a wider area,” says White. “Crusoe is so big that we needed a dense grid to do nice detailed simulations around him that would also affect large wakes behind him. Chris advanced the code so that a high-detail grid along Crusoe’s body affected a lower-resolution grid in the surrounding area within one simulation.”


Compositors lifted an image of the actor riding a jet ski in a water tank from blue screen footage, replaced the jet ski with the digital Crusoe,and fit the actor onto Crusoe’s back.

In addition, the same solver provided underwater aeration so that if Crusoe splashed his flippers or tail under­water, it created bubbles below and foam above. For long wakes, the crew used an in-house wake generator, which creates a 2D simulation.

Then, to create the feeling that water rolled off the adult Crusoe’s skin and that he was always wet, Hill wrote shaders that created an intersection between Crusoe’s skin and a water plane. The shader could generate a meniscus line or an isosurface from which particles rendered as little drops could roll down his surface.

“We had a team of artists working full time on water for the show,” says White. “They matched the water on the set, and made sure the reflections were right and fit into the environment.”
For lighting, Weta Digital usually tries to render shots in Pixar’s RenderMan as full beauty passes, but for this film, they began breaking out lighting passes more than usual to handle changes more quickly.
   
The Environment
In addition to creating Crusoe and the digital water surrounding him, the artists built environments aboveground and below the water that they composited into the plates. For compositing, Weta Digital uses Apple’s Shake, but often calls on The Foundry’s Nuke for environments and set extensions. Aboveground, they extended the water in the loch, placed mountains behind it, and added to the interior of the house. Below water, the crew used an underwater shader to generate a terrain.

“We had a basic model, but Raphael Matto wrote a shader that created the surface by using a complex system that had noise textures feed themselves into other layers of noises,” says White. “He had turbulence, cell noise, fractals, and a lot of very different types of noise. It gave us a great look with a fine level of detail. You could get close, and it would hold up. It didn’t feel like procedural noise.”

All told, the crew worked on the project for approximately one year. “All the shows have really hard things to work out, and this was no exception,” says Letteri. “Although it was fun developing the character, we had to try a lot of things to make sure it held up the whole way. And, water is always technically challenging. There were no short hours on this one.”

Even so, the crew enjoyed the change from the usual type of visual effects work. “This was my first kid show,” says White. “It was fun working on something my little nephews are excited about.” 

Barbara Robertson is an award-winning writer and a contributing editor for Computer Graphics World. She can be reached at BarbaraRR@comcast.net
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