The Polar Express Diary: Part 3 -- The MoCap/Anim Process

David Schaub breaks down some of the key sequences and creative/technical challenges in the latest installment of his exclusive Polar Express Diary.

By David Schaub | Tuesday, February 22, 2005 at 12:00 am

Posted In | Magazines: VFXWorld

Boards Train Sequence (BT)
Number of shots: 30
August 13, 2003-April 12, 2004

August 18, 2003
After the train arrives, the boy opens the front door and runs down the steps toward the train. This action was performed by Tom, but when retargeted to the proportions of a child, the action looks like a slow-motion run on the moon. The reason is that the stride-length for the child is much less than that of the adult who performed the action. However, the timing foot-to-foot (and all of the body language that goes with it) is still in the same time-space as the adult performance. To make the adult-to-child conversion believable, the entire action was sped up by about 12%.

Note When retargeting adults to children, time-scaling became standard practice for broad actions such as running, jumping and other stunts where gravity plays into the equation. Because shot lengths have been defined out of layout, speeding up the action also requires filling in the front and/or back-end of the shot with supplemental animation to make up for the shorter performance that results from the time-scale.

September 26-December 17, 2003
When we first meet the conductor, many of the same problems we experienced with our hero boy are revisited. At this stage there is no pose library, so all of the facial work is done with muscles and tweak clusters. Poses will be added to the library as we move forward. An interesting development is that tweak clusters can now be saved as part of the pose and saved as such in the pose library. The conductor is also equipped with several animatable props, including his hat, glasses, pocket watch and chain. I make a plea to our producers that the watch-chain be simulated by the effects group. Unfortunately their workload is insane as well, so the chain is rigged and the dynamics are animated by hand.

Note 1) A recurring problem with the conductor is that his glasses were constantly being adjusted to assure that the frames were not intersecting his eye-line from the camera’s perspective. The glasses would slide up and down his nose throughout the shots to avoid obscuring the eyes at all costs.

2) Each new hero character (Holly, Know-it-All, Billy, Hobo, Santa, Hero Elves, etc.) went through the same developmental process. It was typical to spend as much as three months on additional controls, deformations and geometric modifications before the first shot of that character is ever finalized.

In the beginning, the addition of other kids to the cast caused Maya to crash with great regularity, costing time and work losses to the production. Originally, Sony’s digital team budgeted the background kids for simple plug-and-play, but they stood out like sore thumbs next to the featured cast. In the end, many hours were put into animating faces away from camera.

Meets Kids Sequence (MK)
Number of Shots: 21
November 11, 2003-March 9, 2004

Up to this point in our story we’ve only dealt with two characters: Hero Boy (Chris) and the Conductor. When we load these two characters into a scene (along with the low resolution train), we still chug along in Maya with a workable amount of computing power and performance. Once we raise the resolution of a character (which is necessary for facial animation), we often bring Maya and our computers to their knees.

The situation became critical once we stepped onto the train-car full of kids.

The typical scene file with just the train and Chris was running upwards of 200 megabytes and when opened in Maya was taxing the computer’s RAM to the tune of 1 gigabyte or greater. Needless to say, our first endeavors to add additional kids caused Maya to crash with great regularity, costing us greatly in terms of time and work losses.