Motion Control of Virtual Humans

omputer animation technologies let users generate, control, and interact with lifelike human representations in virtual worlds. Such worlds may be 2D, 3D, real-time 3D, or real-time 3D shared with other participants at remote locations. Computer graphics techniques let animators create very realistic human-like characters. Although the computational requirements remain significant (especially for real-time generation), the advances in hardware mean that animators can work mostly on the desktop and, in the near future, on the PC. Networking technologies have become more transparent, easy to use, and pervasive, allowing users to treat local and remote information in the same virtual space without considering physical location. Producing and interacting with virtual humans requires an interface and some model of how the virtual human behaves in response to some external stimulus or the presence of another virtual human in the environment. If these virtual humans are avatars (representations of virtual environment users), then the behavior they exhibit should reflect that of their owners, especially if other users in the environment need to recognize them. Programming behavioral models with emotional responses and encapsulating them in virtual humans challenges current research. Computer games successfully implement computer-generated characters in lifelike scenarios. Such games let the characters interact with users. However, the game designers must choreograph in advance every possible action the character might make—users can't generate new movements. Thus the characters' " behaviors " remain fixed and predetermined—they can't respond in new ways to new inputs. Facilitating interesting and engaging responses that reflect the way real humans behave, in real time, remains a major challenge for the field. Traditionally, human animation has been separated into facial animation and body animation, mainly because of lower level considerations. Facial animation results primarily from deformations of the face. Controlling body motion generally involves animating a skeleton, a connected set of segments corresponding to limbs and joints. Using geometric techniques, anima-tors control the skeleton locally and define it in terms of coordinates, angles, velocities, or accelerations. The simplest approach is motion capture. In key-frame animation , another popular technique, the animator explicitly specifies the kinematics by supplying key-frame values whose " in-between " frames the computer interpolates. In inverse kinematics, 1 a robotics technique, the end link trajectory computes the motion of a chain's links. More recently, researchers have used inverse kinetics 2 to account for the center of mass. Although efficient and easily performed in real time, geometric methods often …