Cords: Interactive Modeling of 3D Curves with Physics-Like Properties

A large body of research addresses the representation, construction and interactive control of 3D curves for various applications. Interactively controlling curves with empirical physical attributes of stiffness and elasticity that bend and wrap around 3D scene geometry is a common and challenging problem. In this paper we address this problem with a novel 3D curve called a cord. A cord is created and subsequently controlled in real-time by defining a secondary curve called the guide curve. The guide curve represents the general 3D path that the user wishes the cord to follow while bending and wrapping around scene geometry. Cords have attributes of length, stiffness, and elasticity that allow them to empirically capture a range of behavior from wire to string to rubber bands. Cords that make contact with geometry have a representation in the 2D parameter space of scene objects and can be used not only as geometry for modeling and animation but as 2D parametric strokes for rendering. We present techniques for the creation and interactive control of cords and show examples illustrating their creative use within the animation system Maya.