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Create Surfaces from Other Surfaces (page 374)
Edit NURBS Surfaces (page 448)
Rebuild NURBS Surfaces and Curves (page 449)
Draw Splines (page 210)
Modify Splines (page 274)
Using the Spline tool to create NURBS Surfaces and
Splines
The spline tool is optimized to work with NURBS modeling
NURBS surfaces can be created from a number of 2D objects, including edge
subobjects, polylines, and arcs. But the spline tool is the only object that has
options that are compatible with creating NURBS surface. Not only do splines
consists of Bezier arcs, but they also can be defined with both control vertices
and fit points. The fit points and control vertices offer different editing options
such as knot parameterization and degree options.
Moving Fit Points vs. Moving Control Vertices
NURBS curves have both fit points and control vertices. The fit points lie on
the line, and the control vertices lay outside the line. Use fit points to make
a change to one small part of a curve; use control vertices to make changes
that will affect the shape of the curve as a whole.
Clamp Surfaces and Curves with Open and Closed Geometry
NURBS surfaces and curves can have a clamp, closed, or open form. The form
affects how the object deforms.
â– Open Curves and surfaces - have their start and end CVs in different
positions - it doesn’t form a loop. If you snap the start and end CVs of an
open curve to the same position, it’s still an open curve, because you can
still drag these points away from one another.
â– Closed Curves and Surfaces - a loop with coinciding start and end CVs.
Where they meet is called a seam. If you move one CV, the other moves
with it.
â– Clamp Curve - is a closed loop with a seam that creates extra, unseen
CVs. These unseen CVs can cause the shape to wrinkle and crease when
it is reshaped.
Create 3D Models | 379
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