Feature

Michael Gleicher's paper is part of the session, Animation & Simulation.

Catch Spacetime Swing in the Animation Theater

Norm Badler teaches the course, Virtual Humans: Behaviors and Physics, Acting and Reacting.

Cont...

Shall We Dance?

If you're coming across the term "synthetic actors" for the first time here at SIGGRAPH 98, don't feel like you've somehow fallen out of the cosmic cyberloop. Lots of diverse research can be applied to creating artificial characters, and not everybody uses the term yet.

"I didn't know I was doing it," said Mike Gleicher of Autodesk's Vision Technology Center. Gleicher was unaware of the new specialty until his work was assigned to this conference track. What he thought he had been doing was character animation. He's been solving the problem of how to retarget motion -- taking the movements of one on-screen character and adapting them to another character of different size and proportions.

Why do this? "To reuse motion," Gleicher explains. "Right now, creating motion is very time-consuming and expensive. It only applies to one character. You can't decouple motion from the character--you can't just go out and buy motion."

"What makes the problem hard is that what you want to retain about a motion is not obvious," he says. "What's special about Fred Astaire dancing? Capturing that is mathematically hard."

So far he's settling for the more manageable goal of correcting obvious mistakes in motion. For example, applying motion originally created for tall characters to shorter people could mean that the new characters' feet wouldn't touch the floor when they walked. He says the traditional mathematical approach only makes corrections frame-by-frame, resulting in a person whose foot would suddenly jump down to the floor only in the last frame of the sequence. His technique avoids that problem by solving a mathematical description of the whole sequence of motion.

Another advantage is that his programmed corrections can be universally applied. "'Don't bend your back wrong' applies to all types of motion," he points out, "not just the one you're working on."

Gleicher's animation "Spacetime Swing," demos the method by showing a six-foot woman with heels morphing into a four-foot version of herself while swing dancing with a male partner who bends with her, automatically adapting to her size change. "It's a 47-second summary of the paper," he says.

When you put realistic human renderings together in real time with autonomous AI, you get virtual humans, 3-D characters that both look and act human on demand. The Professors Thalmann are innovators in this part of the synthetic actors field, too, having produced what they claim is the first virtual human in their award-winning 1982 movie, "Dream Flight."

Norman Badler has been working on digital representations of humans even longer, since the 1970s. But the real-time interaction problem has been so difficult, the University of Pennsylvania computer scientist says, "not that many research groups have evolved working, usable systems." Fortunately, cheap, high-powered computers are just now opening that door. "We're starting to see the emergence of pretty decent-looking virtual humans that can serve in a number of applications."

Where the actions of the most lame-brained synthetic actors are totally scripted, virtual human synthetic actors can be ordered around on the fly. "They can respond to commands, they can dance with one another, they can play tennis, they can change the way they walk," Badler explains. "All online in real time as we watch them."

Medic Jack, courtesy of Transom Technologies.

What can they do that's useful? "Jack," Badler's virtual system, has already been enlisted in engineering ergonomics projects to check out whether humans can get along in environments being designed for them. Soldier Jack sits in the pilot's seat of a CAD model of an Apache helicopter, working all the controls. Worker Jack installs a part into a car door on an automotive assembly line. "There you want an accurate body," Badler says, "and different-sized bodies as well. You can make sure those people are going to be able to reach and see and fit. And if they don't, you want to fix the digital environment before you manifest it in plastic and metal."

Medical training is another application. Victim Jack, sprawled on the floor, can be treated by EMS Technician Jack, allowing paramedics in training to make all their fatal mistakes before they get to real victims. Cyberblood runs cheap, but it's infinitely replenishable.