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A team of UCLA researchers is exploring the nexus between motion capture and realistic simulation in a project aiming to develop practical CGI stunt people.

The researchers are designing a modular standalone package that could eventually be incorporated into commercial packages. In keeping with the project’s goal of developing intelligent, autonomous virtual actors, it combines the physical responses of the virtual stuntman with the control of motion capture data.

UCLA’s Ari Shapiro said the team is currently working on plug-ins for the major modelling packages, like 3Ds max and Maya.

"'Complex Character Animation' project is an extension of our virtual stuntmen project where we are attempting to create digital stunt people that can be placed in movies and simulations under situations that would be too dangerous for humans,” said Shapiro.

"Thus, we use a physically simulated environment that allows us to throw our characters off of buildings and impact them with heavy objects. However, unlike simple 'rag doll' environments where characters passively respond to external forces, our characters have motor control and an ability to react to their environments.”

For example, characters that are falling to the ground will twist their bodies and place their hands down in front of them in order to absorb the shock of impact. Also, these characters are given other basic motor skills, such as the ability to stand up from a prone or supine position and will respond autonomously to their environment with whatever skills they are given.

“These motor skills allow a richer interaction between the character and the environment,” said Shapiro “The idea is that motion capture gives you fine-grained control over the motion of an animated character, but doesn't allow the character to interact with its environment, since the motions are completely scripted and don't include a method of modifying the motion according to the objects and other characters that exist alongside the character. "

By providing a mechanism that (1) perturbs the original motion capture data and (2) determines if the characters should continue the original motion or to switch into physical simulation and thus be controlled dynamically (like our virtual stuntman), we now have characters that are ‘truly’ interactive.

“They can now react intelligently to the things in their environment. They can be pushed, poked, hit, placed in a crowd, fight with each other and will act and react accordingly without the need to script their movements. Thus, unlike a video game where characters have prescripted motions and can only interact with the environment in ways that the author originally intended, our characters can behave in previously unseen ways with high-quality motion.”

Like the Massive tool utilised in the production of the Lord of the Rings trilogy, the UCLA system will be able to create large-scale battle simulations, where characters are both aware of the allies and enemies on the battlefield, as well as being able to react realistically to blows that strike various parts of their bodies. However it is designed to concentrate to a greater extent on the subtleties of motion and interaction.

“My understanding is that 'Massive' utilises a database of motion capture to handle the movements and reactions of each character,” said Shapiro.
“Since we use dynamic control, our characters can respond to unique environments and react in novel, unscripted ways. While 'Massive' relies on the AI to develop emergent behaviour among characters, we are using our AI to develop fine grained movements that accurately control the motion among interacting characters.”

The difference being that every character hit in the head with a weapon will react differently according to the angle of attack, mass properties of the weapons, relative velocities of the interacting characters and so forth.
So glancing blows will only briefly perturb the motion of digital warriors, while direct hits might knock them down completely.