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1142 Chapter 9: Sur face Modeling
the number of CVs in the curve. Degree 3 curves
are adequate to represent continuous curves, and
arestableandwellbehaved.Default=3.
Setting the degree greater than 3 isn’t
recommended because higher-degree curves are
slower to calculate and less stable numerically.
Higher-degree curves are supported primarily to
be compatible with models created using other
surface modeling programs.
The number of CVs in a CV curve must be at least
one greater than the curve’s degree.
Automatic Reparameterization group
The controls in this group box let you specify
automatic reparameterization. They are similar to
the controls in the
Reparameterize dialog (page
1–1238)
, with the addition that all choices except
for None tell the software to reparameterize the
curve automatically; that is, whenever you edit it
by moving CVs, refining, and so on.
None—Do not reparameterize automatically.
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
curve or surface changes only locally when you edit
it. With chord-length parameterization, moving
any CV can potentially change the entire curve.
Clo se—Closesthecurve.Disabledifthecurveis
already closed.
Rebuild—Displays the Rebuild CV Curve dialog
(page 1–1237)
, w hich lets you specify how to
rebuild the curve. Rebuilding the curve can change
its appearance.
Reparam.—Displays the Reparameterize dialog
(page 1–1238)
. Reparameterizing a curve changes
the curve’s
parameter space (page 3–1082) to
provide a better relation between control point
locations a nd the shape of the curve.
Tip: Itisagoodideatoreparameterizeafter
youhaveaddedCVstothecurvebyrefiningor
inserting.
Point Cur ve rollout
This additional rollout appears when a point curve
is selected.
Clo se—Closesthecurve.Disabledifthecurveis
already closed.
Editing Surf ace S ub-Obj ects
Modify panel > Stack display > Open the NURBS object’s
hierarchy. > Surface su b-object level > Select surfa ce
sub-objects.
This topic describes cont rols that are common
to point surface s, CV surfaces, and the various
dependen t surface types. A rollout labeled Surface
Common contains the surface sub-object controls
for NURBS surfaces. Another rollout,
Material
Properties (page 1–1150)
, con trols mapping on
surface sub-objects, and is described in its own
topic. See
Surface Approximation (page 1–1241)
for a description of that rollout. The final rollout
forsurfacesub-objectsdependsonthetypeof
surface selected.