8

1156 Chapter 9: Sur face Modeling
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 the other two forms of parameterization,
moving any CV can change the entire sub-object.
CV Curve rollout (modification time)
Degree—Setsthedegreeofthecurve.Thehigher
the degree value, the greater the continuity. The
lower the degree, the more discontinuous the
cur ve seg ments become. The degree can’t b e less
than one or greater than the number allowed by
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 hig her-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 cur ve must be at least
onegreaterthanthecurve’sdegree.
Automatic Re p aram eterization group
The controls in this group box let you specify
automatic reparameterization. They are simi lar to
the controls in the
Reparameterize dialog (page
1–1238)
, with one addition: all choices except
for None tell the software to reparameterize the
curve autom atically; that i s, whenever you edit it
by moving CVs, refining, and so on.
None—Do not reparameterize automatically.
Chord Len g th—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 knots uniformly.
A uniform knot vec tor has the advantage that the
curve or surface changes only locally when you edit
it. With the other two forms of p arameterization,
moving any CV can change the entire sub-object.
Clo se—Closesthecurve.Disabledifthecurveis
already closed.
Rebuild—Displays the Rebuild CV Curve dialog
(page 1–1237)
to let you rebuild the CV curve.
Reparam—Displays the Reparameterize dialog
(page 1–1238)
to let you re parameterize the CV.