A DRIVING FORCE.(motion capture done by Performance Capture Studios)(Technology Information)

A mocap studio test-drives a 3D car `stunt double'

Performance Capture Studios (PCS) in Culver City, California, prides itself on breaking pre-established limits when it comes to motion capture. In the past, the company has not only captured the movements of people and mapped them onto digital characters, but used the technology on unique actors from the animal kingdom, including 5000-pound elephants, a Siberian lynx, monkeys, kangaroos, spiders, and frogs. In a recent project, the "actor" whose motion PCS captured--a car--became the driving force for helping the company establish a new direction in motion capture.

"I believe this is the first complete car capture ever done. We knew it was possible, but just hadn't had a need for it--until now," says Gary Roberts, PCS president. "Most people equate motion capture with human movement for producing similar-looking characters, but we try to push the envelope and show that the technology can be used for driving unorthodox characters with vastly different body topologies to that of an actor."

The studio was approached by the producers of a feature film currently in preproduction (the name of which PCS cannot yet divulge) to test the feasibility of capturing the movement of a car on a live-action set. The client's goal was to map the car data onto a computer-generated vehicle that would replace a physical car in the scene. "They wanted this futuristic-looking car in the film without having to build a physical model, which is expensive," says Roberts. The producers also needed all the interactions of the car with the people and scenery on the set to be realistic and believable. More important, he adds, the live actors had to react and interact with the CG car in a totally realistic way, as the stuntmen crashed into and then rolled over the vehicle.

To accomplish that feat, PCS placed 70 markers on the vehicle to capture the entire physicality of the car for every shot in the test--from the doors and wheels to the fuel cap and suspension. "We placed the markers where we would get good contact points with the actors and scenery when we retargeted the motion onto the CG car," Roberts explains. "Even if the shot called for the car to nudge someone with the bumper, we captured the motion of the entire car, which gives the production team and art director a tremendous amount of options for putting the shot together." For the actual movie though, in some shots PCS may only capture specific portions of the car to make the postproduction easier.

A Perfect Match

Before the actual motion-capture session began, PCS went car shopping, visiting numerous dealerships in search of a production vehicle that fit the physical dimensions of the film's futuristic style of car. This was done so the various parts--tires, hood, trunk, windshield, wheelbase, etc.--occupied the same physical space as the CG version, provided by the client as an Alias|Wavefront Maya model. After selecting a Chrysler LHS, the group was ready to hit the road.