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1114 Chapter 9: Surface Modeling
Fin is h —
Ends creation of the curve, leaving it open
ended.
Create CV Curve rollo ut
This rollout contains the controls for curve
approximation.
Interpolation group
Thecontrolsinthisgroupboxchangetheaccuracy
andkindofcurve approximation (page 1–1238)
used to generate and display the curve.
Draw In All V iewpor ts—Lets you use any viewport
whileyouaredrawingthecurve.Thisisoneway
to create a 3D curve. When off, you must finish
drawing the curve in the viewport where you
began it. De fault=On.
WhileDrawInAllViewportsison,youcanalso
use snaps (page 2–41) in any viewp ort.
Automatic Reparameterization group
The cont rols in this group box let you specify
automatic reparameterization. They are similar
to the controls in the Repar ameterize dialog (page
1–1237), with one addition: all choices except
for None tell the software to reparameterize the
curve automatically; that is, w henever you edit it
by moving CVs, refining, and so on.
None—Do not reparameterize automatically.
Chord L e n g t h —Cho o ses the chord-length
algorithm for reparameterization.
Chord-length reparameterization spaces knots (in
parameter space (page 3–988)) based on the square
rootofthelengthofeachcurvesegment.
Chord-length reparameterization is usually the
best choice.
Unifor m—Spaces the knots uniformly.
A uniform knot vector has t he advantage that the
curve or surface changes only locally when you edit
it. With the other two forms of parameterization,
moving any CV can change the entire sub-object.
Cre at in g NURBS Cu rv e and
Surface Objects
Cr eating Independent S ur f aces
from NURBS Cur ve Objects
To create independent surfaces from top-level
NURBS curve objects, use the Extrude (page
1–680) and Lathe (page 1–707) mo difiers. Extrude
adds height to the curve, creating a shape by
sweepingitalongthecurve’slocalZaxis.Lathe
createsasurfaceofrotation,revolvingtheshape
along a specified axis. You can a lso use the Be vel
(page 1–562) and Bevel Profile (page 1–565)
modifiers on NURBS curves.
These modifiers treat NURBS curves the same way
they treat shapes (page 1–262) .Theadvantageof
using NURBS curves instead of shapes is in the
different poss ible shapes that NURBS geometry
and editing prov ide.
Tip: Whenyoucreateacomplicatedsurface,
especial ly with the Lathe modifier, you often want
to render both sides of the surface. Turn on Force