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| [Figure 9]
Trace over the B-splines to make new even curves. |
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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.
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[Figures 10 & 11]
Use radial curves around the eyes, nose, and mouth (left)to define
surface boundaries. Initial surfaces across the head (right).
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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.
