The merit of a B-rep is that a solid is bounded by its surface and has its interior and exterior . Faces may share vertices and edges that are curve segments. Therefore, a B-rep is an extension to the wireframe model by adding face information to the latter. Topological information provide the relationships among vertices, edges and faces similar to that used in a wireframe model. In addition to connectivity, topological information also include orientation of edges and faces.
Geometric information are usually equations of the edges and faces.
The orientation of each face is important. Normally, a face is surrounded by a set of vertices. Using the right-handed rule, the ordering of these vertices for describing a particular face must guarantee that the normal vector of that face is pointing to the exterior of the solid. Normally, the order is counter clockwise . If that face is given by an equation, the equation must be rewritten so that the normal vector at every point on the part that is being used as a face points to the exterior of the solid.