All images from Inspired 3D Modeling and Texture Mapping by Tom Capizzi, series edited by Kyle Clark and Michael Ford. Reprinted with permission.

Subdivision modeling techniques are used to take a low-resolution polygonal object and increase the resolution using a smoothing algorithm to create a high-resolution model. Several methods work quite well to accomplish this task.

Polygon smoothing is conceptually the simplest type of subdivision modeling. The original polygonal model (Figure 1) is defined as the low-resolution cage, and the higher-resolution geometry is created directly from it (Figure 2). You can use subdivision steps to determine the final resolution of the resultant model. As a rule, the resolution should begin with one single subdivision and increase from there based on the need of the model. The entire model can be subdivided, or selected faces can be subdivided.

	[Figures 1, 2] Polygon smoothing is a predictable and easy way to create a high-resolution model from a low-resolution model.

1. As long as the history is maintained, the model can be returned to the original state by selecting the smooth node and dialing the subdivision number back to 0. Editing the high-resolution mesh, however, will cause unpredictable results if the subdivisions are set back to 0.
2. The resultant geometry type is polygons. Maya has few problems dealing with polygons and will behave in a stable way when using them.
3. UVs are maintained in a predictable manner.

Some disadvantages include the following:

1. Some artifacts can appear at the edges of models because the polygonal density is not high enough. This artifact, called nickeling, can be fixed by increasing the density of the polygons at the edge of the model, or by increasing the number of subdivisions in the smoothing operation.
2. The ability to interactively work on a low-resolution polygonal model while previewing a high-resolution view of the smoothed model is not available in Maya. This can be done, however, using a plug-in called connectPolyShape, which is available at www.highend3D.com. This plug-in can change the way a modeler works and is definitely worth checking out.

Subdivision surfaces use an internal interpretation of the polygonal mesh into another entity type. This entity type behaves similarly to NURBS surfaces. The easiest way to understand this process is to look at Pixar’s RenderMan, which creates subdivision surfaces.

Within a low-resolution cage are quadrangles and triangles. In RenderMan, these entity types are treated differently. A quadrangle is assigned a NURBS surface. Every quadrangle in a polygonal mesh has an infinitely smooth surface that is tangent to the adjacent surfaces. At render time, these surfaces are tessellated adaptively at a pixel level. This unique tessellation method allows for unbelievable detail when rendering displacement maps on relatively simple surfaces.

Triangles, however, are not defined as NURBS surfaces. They are defined as subdivided triangles, in a similar way that smoothed polygons behave. The ability to tessellate adaptively is reduced.

Maya behaves differently than RenderMan. The geometry can still displace better than any smoothed polygon model, and the areas where quads transition into triangles are treated differently.

These points can be seen as advantages that subdivision surfaces in Maya have over smoothed polygonal models.

Other advantages include the following:

1. Interactive editing of low-resolution polygonal cage while previewing high-resolution geometry without using plug-ins.
2. Many tools that allow quick editing, mirroring and conversion of subdivision surfaces.