CG Modeling 3: Advanced - An Introduction to Computer Graphics for Artists - page 273

Fig. 15.1 This bicycle frame is built from a single subdivision patch. It renders easily and is fairly
easy to make compared to working in NURBS or polygons, but is less accurate than NURBS and
less effi cient than polygons

surfaces are not as fl exible as polygons because the mesh still has some topological
constraints by which it must abide. It is less constrained than NURBS patches, mak-
ing it easier to use than NURBS in many ways, but some polygonal tools will not
work on a subdivision surface.

15.2.2 Control Mesh and Surface

When editing subdivision surfaces, you will be able to work on the low res con-
trol mesh or the high res surface (Fig. 15.2 ). The control mesh is a coarse group
of polygons that topologically resembles the fi nal surface you are editing, but
will look noticeably different from the fi nal object due to edge smoothing values
and continuity.

15.2.3 Subdivisions and Solids

A solid is a polyset that has height, width, and depth and is closed on all sides. A
plane or grid primitive is not a solid because its topology is open. A sphere, cube,
cylinder, and torus are all solids because their topology is closed. Subdivision sur-
faces can be made from any of these primitives, regardless whether they are open or
closed. Subdivision surfaces may have arbitrary topology, meaning there are no
special problems associated with the genus of the model, no matter how high or low
the value (Sect. 14.1.3 ) (DeRose et al. 1998 ).