Unrepresentative vertex normals - Modeling and Rendering
Calculated vertex normals may not adequately present the surface's geometry. For illustration, if we calculate vertex normals through averaging the normals of the surfaces sharing a vertex, all of the vertex normals of the figure that will be parallel to the other, resultant in little or no variation in shade whether the light source is distant. Subdividing the polygons additionally before vertex normal computation will resolve this problem. Though these problems have prompted more work on rendering algorithms which handle curved surfaces directly, polygons are sufficiently quicker and also easier to process such they now form the core of main rendering systems.