Graphics Reference
In-Depth Information
Fig. 14.17
The surface on
left
was made by revolving curve
1
. The surface on the
right
was built
out of curves
1-4
. Other surfaces could be made from any one or combination of the four curves
shown here, depending on the tool used
all tools build surfaces with just the four basic options mentioned above, tool selection
decisions should be easier to make. In polygons, the most important thing to remem-
ber is that your vertices need to be in the right place. With NURBS, it is your control
points. No matter how many options you have, it always comes down to that. If you
have to, you can always move the points using simple transform tools.
14.4
Surfaces
14.4.1
Introduction
A NURBS surface is a
parameter-based object
, meaning that it may be edited by
modifying parameters. A
parameter
is a variable that can be modifi ed to change the
shape, position, orientation, or surface type of your object. A NURBS object con-
tains the following editable variables:
•
Edit point position
•
Control vertex position
•
Control vertex weight
•
Number of knots
•
Tangent length
•
Tangent direction
•
Continuity
•
Number of isoparms
•
Position of isoparms
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