Flyin' High

Artists create realistic reindeer for a new Christmas movie

By Karen Moltenbrey

Can reindeer really fly? Absolutely, maintains Jerry (Richard Thomas), a college professor in Flight of the Reindeer, a two-hour CBS holiday special airing December 17. In the live-action movie, a youthful Jerry credits a flying reindeer with saving him when he falls from a tree. Now a grown-up, Jerry is determined to turn doubters into believers by proving that reindeer are indeed capable of flight. Is he successful? Yes, thanks to the artists at CBS Animation (Hollywood), whose job was to create realistic CG flying reindeer that blended seamlessly into live-action scenes.

"The entire story focuses on the ability to believe, so it was crucial that our reindeer models and animation looked 100 percent realistic," explains Craig Weiss, CBS Animation's visual effects supervisor for the project.

The first step toward accomplishing this goal was building an accurate digital model of the animal. To ensure that the deer's head, face, and mouth were correctly proportioned, modeler Scott Snyder digitally scanned the upper portion of an actual reindeer, provided by a taxidermist, using a Cyberware (Monterey, CA) 3D scanner. He then converted the point cloud data into a patch-based surface with Paraform's (Santa Clara, CA) NURBS modeling software.

For the body, exact measurements were not as important as was the flexibility to make necessary changes to that portion of the model during the animation process. So Snyder hand-sculpted the animal's torso and limbs with Alias|Wavefront's (Toronto) Maya and PowerAnimator, using photographs and anatomy books for reference.

The most time-consuming part of the modeling-and the project in general-was creating a finished fur coat, which involved a laborious, multistep process. To make the fur lie in the correct direction, the group used approximately 200 curves as guiding elements that ultimately directed the million-plus hairs generated on the fully furred deer. To facilitate this task, the development team, led by senior software developer Ben Masek, scripted a program, integrated into Maya, that automated the procedure. Once the guide curves were oriented, the group used Alias|Wavefront's StudioPaint to create the hair color, overall density, and length. Finally, the group applied dynamics to the guide curves. "To add realism to the fluffier parts of the hair [such as the deer's beard], we applied Maya dynamics to the longer guide curves so the beard would move when the wind blew through it," explains Masek.

Crucial to the story line of a new holiday TV special was the believability of flying reindeer. This required digital artists to model, animate, and composite realistic computer-generated deer seamlessly into the movie's live-action scenes. (Images courte

To individualize the look and feel of the reindeer, the modelers provided a different color pattern for each of the nine animals, along with a unique set of antlers. To vary the size of each deer, Snyder added a scalar node to the skeleton hierarchy.

"Creating realistic fur with the right clumping and hair length took a lot longer than we had anticipated, but in the end, it looked fantastic," says Weiss. However, the hour-plus it took to render each frame was impractical, given the team's seven-week deadline.

"We started off with the Rolls Royce of hair, but when reality set in, we realized we didn't need all the nuances and details that we had added," Weiss explains. "We needed to be realistic about rendering time and remember the fact that we were doing this for television, which is a lot more forgiving than big-screen feature films. So we found ways to elegantly cheat to help us complete the project by airtime, such as adding motion blur to the hair and eliminating the self-shadowing."

To create a more lifelike appearance for the reindeer, the artists modeled the animals in Maya and PowerAnimator, where they also added jiggle to the skin and muscle structure.

To further reduce the rendering drain, the animators limited the dynamics to achieve a wind-blown effect for the deer's manes and beards only, rather than for their entire bodies, where it likely would have been unnoticed. "However, running the dynamics through the curves in the hair and adding jiggle to the skin and muscles made a tremendous difference in the animals' appearance-it brought them to life," says Weiss. "Without it, they would have looked like stuffed reindeer."

Even though the models took a great deal of time to create, the most arduous task, according to Weiss, was creating an animation sequence that looked as if the reindeer were flying, not galloping. "Traditionally, all the Christmas movies portray reindeer as docile, slow-trotting animals when they pull Santa's sleigh, which is stuffed with toys," he says. "We wanted to provide more dynamic, realistic motion as they pulled this large, heavy sled."

To make the digital deer move, Snyder used a combination of forward and inverse kinematics in the character setup. However, creating the flying cycle proved more complicated. "The reindeer had to look like they were flying, not running, but they still had to look like reindeer, so we couldn't alter their movement too drastically," says Niel Wray, CG supervisor. After viewing videos of galloping and swimming horses and running deer, the animators decided on a hybrid galloping-swimming motion.

Using digital storyboards and previsualization helped the animators integrate the CG reindeer into the live-action scene.

To ensure that the CG reindeer fit seamlessly into the live action, the animators created animatics (CG storyboards) in Maya to help them previsualize the scene. For generating the movements of the actual sleigh prop during the flying sequences, the team used a six-axis motion simulator base, along with a motion-control camera system. "We were able to previsualize the motion from the sleigh in 3D and match the camera moves, so when it came time to drop in the reindeer, everything lined up perfectly," says Weiss.

Apparently with the right help, reindeer really can fly.

Maya Dynamics, Alias|Wavefront (www.aw.sgi.com)