Automatic joint and skeleton computation for the animation of sketch-based 3D objects

Animated models are essential for simulations and virtual worlds. In many applications approximate models are sufficient and an efficient model creation and animation suitable for untrained users is required. Sketch-based modelling has been shown to be a suitable interface for creating such models because the underlying pen-and-paper metaphor is intuitive and effective. However, there is no similarly easy process for animating these models. In this paper we present an automatic skeletalisation and rigging algorithm for sketch-based models. Our algorithm analyses sketched contours and creates fully automatically a hierarchical skeleton with joints. The surface mesh is bound to the curved skeleton bones using skinning techniques and the resulting model can be animated using skeletal animation techniques. Our analysis and user evaluation suggests that the joints placements are perceived as natural. The models can be animated using traditional skeletal animation techniques such as key-framing and motion capturing, or can be used as input to physically-based animation techniques and evolutionary algorithms.