Motion Capture Lab

Last Monday, we visited the Motion Capture Lab of CMU. It was the first time I've seen a real-time demo of motion capture.

It was just amazing to look at the instantly rendered model moving as the researcher moves. I've also looked at the markers closely. They are just spheres made from plastic. Nothing fancy. But there are surprisingly many sizes for them. At first, I was wondering how does the system distinguish markers of different sizes from such a long distance when they are used at the same time. And I found the answer later: the system need not distinguish different markers. As long as it recognizes the marker, it works to capture the motion of that point. On the other hand, for general purposes, larger markers are preferred, because they are easier to be spotted no matter from which direction. The smaller markers are used only in special cases to deal with sophisticated motions, like for hands or facial expressions. In this case, some special preparations and processes might be needed, so it's likely that markers with large size difference are not used at the same time. Well, I might need some citations here to prove my assumption.

I also got some fun facts about motion capture in this trip. I didn't know that static objects can be motion captured too. And it is actually preferred to capture the objects in the scene to determine the positions for the models later. Sometimes, the motion captured is totally different from what we see in the final animation work. For example, the motions of a dog and the motions of infants in the animation are all from motions captured from adult human actors. Also, additional facilitators are used to invigorate the motions. For instance, toggle the ball to an elastic string to enhance its bounciness.

The mocap lab is also cooperating with robotics lab to capture human motions for programming the robot motions. I think while this is a good way to make the movements more natural, ie. more like human, it might not be as effective as expected. Human body movement seems natural because the movements are generated naturally from the body structure. It might hardly seem natural for the robot with different body structure from human. Also, the weight distribution of the robot should be very different from human, so it is challenging to maintain its balance with human motion embedded.

In a nutshell, it was a fun experience to visit the lab. I hope I will get a chance to try it out for my project in the near future.