An Automatic Collision Response Algorithm

Many animations depict two or more objects interacting and potentially colliding. Collision response is a complex process if the objects are intended to respond like soft bodies and to exhibit the properties of real objects. Physically-based models calculate contact forces to incorporate into the calculation of velocities and positions of the control mesh. Some physically-based models, for example those that model cloth, strive for visually realistic results. Until recently the magnitude of the calculations required for physically-based modeling have precluded real-time interaction. A complaint with physically-based models is the correlation between the parameters, such as forces and torques, and the resulting 'look' of the response are sometimes di cult for the user to understand. The work presented in this thesis does not strive for the simulation of real object properties. Instead it tries to remove the interpenetration between two objects while providing a set of controls for the animator to adjust the 'look' of the collision response. A set of data points within the interpentration region of the two colliding objects is determined by the algorithm and each object interpolates those data points to remove the interpenetration. The position of the data points is a function of the relative rigidity of the two objects. Locality or globality of the response is achieved by allowing the user to specify the amount of response absorbed by di erent levels of a hierarchical B-spline modeling primitive. Combinations of deformational, translational and rotational collision response mechanisms give more