Guidelines for Planning Surfaces:
1. Use as few surfaces as possible.
While it will be difficult to keep the number of surfaces as small as you would prefer, you should strive to keep the number of surfaces as small as possible. When you are texture mapping a model, you will have to deal with each surface as a separate map.
This is a good argument for converting to polygons at the end of this process. While polygons are somewhat less flexible during animation, and harder to set-up than NURBS surfaces, the ability to assign one map across multiple polygon patches can easily make up for the lost time in additional set-up problems.
2. Never create a triangle.
In nature, there are many places where the natural flowlines of the contours of the face seem to come to a point. Shown below is an example of how a person may wish to create the natural flowlines of a face by creating surface boundaries that come to a point at the corner of the eye.
This may seem like a convenient way to define an area, this will give you many problems later.
3. Use five-cornered intersections.
Please examine the diagram below.
The surfacing pattern shown in this eye diagram cam be used at eye location, arm locations, hip locations, mouth locations, and anywhere else a round object will appear out of a larger smooth area.
It is important to note 2 specific things about the diagram above.
3a. The 5-corner intersection:
The intersection shown above has 5 surfaces coming together at one point. Using this technique allows multiple surfaces to be introduced into a regular grid of surfaces without introducing triangular patches.
When you align surfaces later, you will need to use special techniques to maintain tangency across this special condition.
3b. Do not introduce patch boundaries in areas of detail.
When laying out surfaces, a person may be tempted to create patch boundaries
that define details. This is generally not a good idea. When you are trying
to maintain tangency across surfaces in areas of detail, you will find
that you do not have as much control as you need to keep detail AND maintain
tangency. Try to create detail from the surface, and introduce patch boundaries
across areas of the LEAST detail. Detail can be added by adjusting CVs
or by increasing isoparms if necessary.