PhysIK: Physics based Inverse Kinematics for Character Posing and Animation

Abstract

Posing and animating rigs can frustrating for animators. Among the tools they use to make things easier, inverse kinematics solvers calculate the relative rotations of rigid bodies connected by di erent types of joints which is useful for both robotics and animation. However, when posing a rig for 3D modeling and animation, some inverse kinematics solvers can produce unpredictable and unintuitive results, especially for large displacements. Along with the issues above, IK solvers are also limited in their ability to create dynamic poses. It can take a large number of target point speci cations to create a pose or animation that has feasible secondary e ects. For example, when a person walks, the legs are not the only parts of the body that moves, but the arms, torso, and head all move in reaction. PhysIK is a physics-based character posing and inverse kinematics algorithm inspired by how artists manually pose wooden mannequins. To pose a wooden mannequin, the artist just has to move it into place. Part of what makes it so easy to use is that we have an intuitive sense of how physical objects work. Objects in the real world do not jump around or pass through themselves. In order to capture this intuition, PhysIK simulates physics on a rig to move the rig into the desired con guration. By taking into account the form and mass of the rig, PhysIK can accurately simulate plausible secondary motions. For this reason, PhysIK is useful for animation as well as static posing. In addition, with a physics-based simulation, there is no need to worry about whether a solution exists. Even if the target pose is impossible, the simulation will not break down. Instead, it will nd a good compromise between what the user speci ed and what is physically possible.