The HalfEdge object is the directed side of the edge of a Shape object. An edge has two half edges. You can transverse the contours of a shape by "walking around" these half edges. For example, starting from a half edge, you can trace all the half edges around a contour of a shape, and return to the original half edge. Half edges are ordered. One half edge represents one side of the edge; the other half edge represents the other side.