By: John Michael Pierobon
In my last column I wrote about rendering and ray tracing in computer animation. That is only part of what goes into making a good animation. Here I want to discuss kinematics and artificial life.
Kinematics is very heavily used in animation. Kinematics is the branch of mechanics that deals with motion in the abstract without regard to force or mass.
Computer animators use kinematics to model how someone would walk, or run. Animators need to program their computers so that their action hero does not hyper extend his or her knee.
Animators try to be as realistic as possible. They obtain data from real time motion capture devices. These devices capture the (x, y, z) coordinates of a person's hands, elbows, knees, ankles, shoulders, hips, and head in real time. The person, or actor, with the motion capture devices performs a series of activities such as running up some stairs, or dancing, which are captured on to a computer. Knowing the coordinates of the actor's head, arms, legs, etc. allows the animator to map that on to an animated figure. The animated figured is then programmed to move its arms and legs just like the actor did. Where do you think the dancing baby on "Ally McBeal" and "Cyber Lucy" learned how to dance?
Computer games are now programmed where for example an action figure is programmed to walk across the room while avoiding a low beam. The animated figure will detect the low beam in its path and switch from walking normally to ducking to avoid the beam.
These activities, such as dancing or ducking, are called "behaviors". Animated characters can be programmed to have certain behaviors, and to acquire new behaviors. This is called "artificial life".
There is a hilarious short animation called "Sid and the Penguins". When Sid comes out of his igloo, six nearby penguins are programmed to act naturally. All six penguins have the same set of behaviors in the repertoire, but each chooses one at random. So sometimes some penguins do the same thing, sometimes not.
One of the behaviors an animated character can have is to follow the behavior of the lead character. In Disney's "Mulan" when the horses gallop off the cliff, the horses are following the behavior of the lead horse. In this particular scene, there is true use of kinematics, for some of the effects of gravity are ignored.
This follow-the-leader behavior is also used in "Antz". Other movies such as "101 Dalmatians" also used it, but injected some random variables.
Merging the concepts of behaviors, kinematics and artificial life can lead to some interesting simulations. For example, how would a crowd react to a fire in a movie theater? Computers could be used to simulate this, and determine if there are enough fire escapes before the movie theater is built. This could save lives.
So good things can come out of computer games and animation.