Motion transformation by physically based spacetime optimization

Automatic generation of realistic human motion has been a long-standing problem in computer graphics. This thesis introduces a novel algorithm for transforming character animation sequences that preserves essential physical properties of the motion. The algorithm maintains realism of the original motion sequence without sacrificing the full user control of the editing process. We use the spacetime constraints dynamics formulation to manipulate the motion sequence. In contrast to most physically based animation techniques that synthesize motion from scratch, we take the approach of motion transformation as the underlying paradigm for generating computer animations. In doing so, we combine the expressive richness of the input animation sequence with the controllability of spacetime optimization to create a wide range of realistic character animations. The spacetime dynamics formulation also allows editing of intuitive high-level motion concepts such as the time and placement of footprints, length and mass of various extremities, joint arrangement and gravity. Our algorithm permits the reuse of highly-detailed captured motion animations. In addition, we describe a new methodology for mapping a motion to/from characters with drastically different number of degrees of freedom. We use this method to reduce the complexity of the spacetime optimization problems. Furthermore, our approach provides paradigm for controlling complex dynamic and kinematic systems with simpler ones.