8

NURBS Curves 1107
Generate Ma pping Coordinates—
Generates
mapping coordinates so you can apply mapped
materials to the surface.
The Generate Mapping Coordinates control is
present on the Modify panel. It is at the Surface
sub-object level.
Flip Normals—Turn on to reverse the direction of
the surface norma ls.
The Flip Normals control is present on the Modify
panel. It is at the Surface sub-object level.
When you modify a CV surface, a rollout lets you
change its
surface approximation settings (page
1–1241)
.
Automatic Reparameterization group
Theradiobuttonsinthisgroupboxletyou
choose automatic reparameterization. With
reparameterization, the surface maintains
its parameterization as you edit it. Without
reparameterization, the surface’s parameterization
doesn’t change as you edit it, and can b ecome
irregular.
None—Do not reparameterize.
Cho rd L e n g t h —Chooses the chord-length
algorithm for reparameterization.
Chord-length reparameterization spaces knots
(in
parameter space (page 3–1082) )basedonthe
square root of the length of each curve segment.
Chord-length reparameterization is usually the
best choice.
Unifor m—Spaces the k nots uniformly.
A uniform knot vector has the advantage t hat the
surface will change only locally when you edit it.
With the other two forms of parameterization,
moving any CV can change the entire surface.
NURB S Cur ve Primitives
NUR B S Cur ves
Create panel > Shapes button > NURBS Cur ves
NURBS (page 3–1074) curves are Shape objects
(page 1–257)
,andyoucanusethemasyou
do splines. You can use the Extrude or Lathe
modifiers to generate a 3D surface based on a
NURBS curve. You can use NURBS curves as
the path or the shape of a loft. (Lofts created
using NUR BS curves are loft objects,
not NURBS
objects.)
You can also use NURBS curves as Path Constraint
and Path Deform paths or as motion trajectories.
You can assign thickness to a NURBS curve so it
rendersasacylindricalobject. (Thethickened
curve renders as a polygonal mesh, not as a
NURBS surface.)
A curve and the same cur ve rendered with thickness
There are two kinds of NURBS cur ve objects:
Point Cur ve (page 1–1108)
CV Curve (page 1–1112)
Like other Shape objects, NURBS curves can
contain multiple sub-objects, which are either
dependent or independent.
Creating Cur ve Sub-Objects (page 1–1153)
Creating Surface Sub-Objects (page 1–1179)