Using Skinned Surfaces to Design Swept Surfaces
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This page is for your reference only. Since this software
component is still under development and testing,
it is stable. So, use it
with care.
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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.
Operations
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:
- Next Instance moves to the
next instance (of the profile curves). If this instance is the
last one, the next instance becomes the first. The current
instance is always shown in thick line.
- Previous Instance moves to the
previous instance (of the profile curves). If this instance is the
first one, the previous instance becomes the last.
- Make Instance creates a new
instance between this and the next instances. To move to the newly
created instance,
use Next Instance.
- Slider Position can be used
to adjust the position of the current instance along the
trajectory curve.
- Slider Scale can be used
to scale the size of the current instance.
- Slider Rotate can be used
to rotate the current instance about the
X,
Y and
Z axes. Showing the
coordinate axes and rotating the scene will help rotate instances
correctly,
- Generate Surface will
produce a skinned surface that interpolates all instances and
export the surface representation to the surface system.
- Do not
Dismiss this
Profile Instance Control window until you are
satisfied with your design. Once you close this window, even
though your have saved your scene, the current design is lost.
If you load the scene back, you just have a set of curves rather
than a scene organized for designing swept surfaces using
skinning.
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.
Example
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.
