# Skinned Surfaces

A *skinned surface* is surface that contains a given set of
curves *C*_{1}(*u*),
*C*_{2}(*u*), ...,
*C*_{n}(*u*). Note that the construction
of a skinned surface is not unique. Different constructions provides
different skinned surfaces. Note also that the order of the given curve is
important; changing the order yields a different skinned surface.
The given curves describe the shape of the desired surface, and hence are
called *profile curves*. Since a skinned surface contains all
of its profile curves, it *interpolates* the given profile curves.

To design a skinned surface, select
**Advanced Features** followed by
**Cross Sectional Design**. This will
bring up the curve system. In the curve system,
design the profile curve in the desired order and make the first curve to be
the current curve. Then, select
**Techniques** followed by
**Generate Skinned Surface**.
The surface system will display a surface defined by the given profile curves.

This system will interpolate the profile curves using second degree surfaces.
As a result, the number of profile curves must be at least
three. **The degree for the skinned surface can be
selected in a future version.** Since there are in general many
curves involved, it would be easier to design each curve in turn. After
designing a curve, save it to a file. Then, use
**File** followed by
**Import Scene** to load these curves back
in the desired order.

### Example 1: A Simple Skinned Surface

Let us try a simple surface first. The following shows four NURBS curves of
degree 3. The one in black is the first curve, while the leftmost one is the
fourth curve. Click **here**
to download a copy of this file
(**skinned-1.dat**) for your practice.

The following shows the generated skinned surface, which contains the four
give profile curves. Note that the control points of the generated skinned
surface are different from those control points that define the four profile
curves. Instead, the control points of the generated skinned surface are
computed from the control points of the profile curves.

### Example 2: A Tube - Again

With skinning, one can design a more complex tube. Six circles are arranged
so that the generated surface would look like a pipe turning 90 degree.
The left most circle in black is the first profile curve.
Click **here**
to download a copy of this file
(**skinned-2.dat**) for your practice.

The following are the generated skinned surface. It does not look like
very smooth. But you can make it better by adjusting the circles.

### Example 3: A Complex Skinned Surface

The following figure contains nine NURBS curves of degree 3 that
approximately resemble the shape of a car body. You can adjust these
profile curves to make the design more realistic. The left most curve in
black is the first profile curve.
Click **here** to download a copy of this file
(**skinned-3.dat**) for your practice.

The following shows the generated skinned surface.