SHAPE-DEPENDENT MOTION INTERPOLANTS FOR PLANAR OBJECTS

Rigid body kinematics is most commonly about movements of unbounded spaces. This paper deals with the kinematics of bounded shapes in a plane and focuses on the problem of motion interpolation of a planar object with its shape taken into consideration. It applies and extends a shape-dependent distance measure between two positions in the context of motion interpolation. Instead of using a fixed reference frame, a shape-dependent inertia frame of reference is used for formulating the distance between positions of a rigid object in a plane. The resulting distance function is then decomposed in two orthogonal directions and is used to formulate an interpolating function for the distance functions in these two directions. This leads to a shape-dependent interpolation of translational components of a planar motion. In difference to the original concept of Kazerounian and Rastegar that comes with a shape-dependent measure of the angular motion, it is assumed in this paper that the angular motion is shape independent as the angular metric is dimensionless. The resulting distance measure is not only a combination of translation and rotation parameters but also depends on the area moments of inertia of the object. It derives explicit expressions for decomposing the shape-dependent distance in two orthogonal directions, which is then used to obtain shape-dependent motion interpolants in these directions. The resulting interpolants have similarities to the well-known spherical linear interpolants widely used in computer graphics in that they are defined using sinusoidal functions instead of linear interpolation in Euclidean space. The path of the interpolating motion can be adjusted by different choice of shape parameters. Examples are provided to illustrate the effect of object shapes on the resulting interpolating motions.