Using Skinned Surfaces to Design Swept Surfaces

As mentioned in the discussion of swept surfaces, if a profile curve is rotated and scaled, the resulting swept surface may not have a NURBS representation. As a result, this system only allow to translate the profile curve; but, this limits the power of swept surface generation. To overcome this limitation, this system implements the construction of swept surfaces using skinning. More precisely, a user first designs a trajectory curve and then places a number of transformed (i.e., rotated and scaled) instances of the profile curve along the trajectory curve. Then, a skinned surface is constructed to interpolate all of these transformed instances. This skinned surface is not the actual desired swept surface; it is only an approximation.


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 a profile curve and a trajectory curve, and make the profile curve the current curve. The curve system always uses the current curve as the profile curve. Then, select Techniques, followed by Generate Swept Surface, followed by Using Skinning. A Profile Instance Control Window appears and a number of profiles are attached to the trajectory curve.

The meaning of each button in the Profile Instance Control Window is as follows:

On the drawing canvas of the curve system as shown above, a few instances of the profile curve are attached to the trajectory curve. In fact, to create an instance, the first point (i.e., P(0) - if P(u is the profile curve) is attached to the trajectory curve, and the instance is generated by translating along the profile curve to a proper position. The original design of the profile curve is also shown.


The following shows seven profile instances (in black) along the trajectory curve (in blue). Click here to download a copy of this file (sw-sk-1.dat) for your practice. Recall that it is mentioned above that loading sw-sk-1.dat into the curve system will not provide you with the configuration above. A little practice is required to regenerate the scene.

The following are the generated skinned surface, which contains all seven profile instances.