Rademacher proposed the method that a three-dimensional structure is used in cel animation.[Pau99a] The reference hand-drawn image of the object or character often contains various view-dependent distortions that cannot be described with conventional 3D models. Therefore, to prepare view-dependent models, which consist of a base model, a set of key deformations created by the base model, a set of corresponding key viewpoints, and a given discretional viewpoint, they interpolate the key deformations that are specific to the new viewpoint. They thus capture the view-dependent inconsistencies of the reference drawing.