Tripartite Line Tracks Qualitative Curvature Information

We present a qualitative shape description which has previously been proven to be useful for object categorisation. The description is based on a set of shape primitives which we will restrict to a new subset of relations representing stylised curvature information. In contrast to other qualitative shape theories, this description enables us to distinguish different convex shapes. This is especially interesting from a cognitive point of view since these shapes show salient visual differences. It turns out that the distinction between two sides of a line together with the distinction between acute and obtuse angles make up a powerful concept of orientation information for shapes in two dimensions.