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created with 4 control vertices have the same shape as Bezier curves of degree
3 as shown on the right.
You can close a spline so that the start point and end point are coincident
and tangent. By default, closed splines are mathematically periodic, meaning
that they have the smoothest (C2) continuity at the point of closure.
In the example, both splines are closed, and the point of closure is marked
with a dot. The result of setting the SPLPERIODIC system variable to periodic
is shown on the left, while the result of the legacy setting is shown on the
right.
NOTE The legacy method for creating B-splines by creating a polyline, and then
using the Spline option of the PEDIT command generates only an approximate
spline-fit polyline.
See also:
Modify Splines (page 274)
Break and Join Objects (page 270)
Create Solids and Surfaces from Lines and Curves (page 342)
Draw Helixes
A helix is an open 2D or 3D spiral.
You can use a helix as a path with the SWEEP command. For example, you
might sweep a circle along a helix path to create a solid model of a spring.
214 | Chapter 6 Create and Modify Objects