[Figures 30 & 31] The low-resolution model (left) created from the NURBS surfaces. The final high-resolution polygonal model (right) used for rendering.

Wrap Deformer
A wrap deformer is commonly used for complex character setup for animation. A model created for this kind of deformer is a low-resolution polygonal mesh or a low-resolution NURBS shape that accurately describes the high-resolution model. The common practice is to bind the skeleton of the character to the wrap deformer, and then bind the high-resolution mesh to the wrap deformer. The wrap deformer can be weighted easily, so the binding to the skeleton is efficient and accurate. Because the wrap deformer is created from the surfaces of the high resolution mesh, the points along the adjacent surfaces where the mesh usually falls apart is bound by a common series of points that fall precisely where the points on the surface meet, ensuring that the mesh stays together at the correct places.

High-Resolution Polygon Settings
Using the exact setting options described previously, but filling in the number of subdivisions per span to a higher number, such as 3 or 4, creates a high density mesh for rendering as polygons. This is the process that was used to render this model, because the rendering pipeline at Rhythm & Hues only supports polygons, not NURBS surfaces. 31 The NURBS surface construction allowed for the proper placement of polygonal geometry for animation, texturing and setup. The resultant model was extremely clean and was fast to build because, of the NURBS controls. Figure 31 shows a shaded view of the final model.

Tessellation Settings
When rendering using Maya, pay careful attention to tessellation settings. The best way to adjust settings is to use the Attribute Spread Sheet.

The settings that work best for patch models is the explicit tessellation option, which sets a specific number of tessellated polygons to be generated at render time based on the spans in the surface being rendered. When the spread sheet is opened, the column under explicit tessellation attributes should be highlighted then turned to on. It will then be necessary to scroll over the Number Per Span U column and Number Per Span V column and adjust the explicit settings to appropriate values for that scene.

For models that are not built with patch modeling techniques, adjusting the tessellation parameters for the entire model is a bad idea. However, surfaces in patch models usually have spans that are relatively equal in size across the model, which allows the tessellation settings to be set using the Number Per Span options for the entire model. It may be necessary to adjust the tessellation settings differently for different surfaces if the spans for those surfaces get unusually large or small compared to the rest of the model.

To learn more about character modeling and other topics of interest to animators, check out Inspired 3D Modeling and Texture Mapping by Tom Capizzi; series edited by Kyle Clark and Michael Ford: Premier Press, 2002. 266 pages with illustrations. ISBN 1-931841-49-7. ($59.99) 

Tom Capizzi