[Figure 9] Trace over the B-splines to make new even curves.

Drawing the Curves
Starting with the lines created in the previous steps, new curves are constructed. These curves can be created by manipulating, detaching, attaching and rebuilding the converted B-splines that were created earlier or by tracing over existing curves. The first step is to create flow lines that go across the entire head. Starting from the mouth and eyes, draw NURBS curves from the edges of the radial mouth and eye regions toward the back of the head. These lines will be used later during the construction of the initial surfaces. In Figure 9, the curves shown in red were created by tracing over the existing data. These lines were constructed as long, continuous curves to create large surfaces over the head.

Here are some additional tips on creating usable splines for a curve network:

• Use edit points to draw splines wherever possible. While you draw splines across other splines, you will need to connect splines to each other. Only edit points can guarantee that the splines will intersect.
• Draw continuous splines across the entire model whenever possible so that you can visualize the changes in the surface while maintaining smoothness across the model. If you create short splines that meet in the middle of the model, there will be a break in the continuity of the surfaces.
• Next, create radial curves to define surface boundaries. Using the flow lines created in the previous step, radial lines are created that begin to define the areas that are to be turned into individual patches. Edit point curves were used to create the radial curves. The points where the curves come together are certain to intersect. In Figure10, radial curves around the mouth, eye and nostrils allow surfaces to be constructed correctly.

[Figures 10 & 11] Use radial curves around the eyes, nose, and mouth (left)to define surface boundaries. Initial surfaces across the head (right).

Patch Modeling Head
Surfaces for this model were created in two steps. The first step was creating surfaces that cover the head. I called these “initial surfaces.” The last surfaces are called “final surfaces,” which are the initial surfaces broken up into surfaces that have all of the isoparms aligned. The term patch modeling was derived from these smaller surfaces. The smaller surfaces are all “stitched” together in a patchwork of surfaces that make up the 3D character.

Initial Surfaces
The head is the focus of the first part of the tutorial because the face has the hardest transitions for modeling. No effort was made to get the “initial surfaces” to have isoparms that align; the plan was to do this later. The most important focus of the initial surfacing phase was to have the surfaces have tangential continuity and smoothness.

Bi-rail surfaces were used almost exclusively to create the surfaces on the side of the head because they allowed me to make large patches that covered the majority of the head quickly. The larger surfaces would be broken up into smaller regions later. Using smooth curves that sweep across the entire face create a smooth surface network without using tangency tools. These initial surfaces of the head are constructed so the surfaces are smooth, but the alignment of isoparms is not considered until later.