9
1154 Chapter 9: Surface Modeling
To lift a CV off the construction plane, use
the
Ct rl key as described earlier in this topic
under "Draw ing T hree-Dimensional Cur ves."
As with splines, if you click over the curve’s
initial CV, a Close Curve dialog (page 1–1228)
is displayed. This dialog asks whether you
want the curve to be closed. Click No to keep
the curve open or Yes to close the curve. (You
canalsocloseacurvewhenyouedititatthe
Curve sub-object level.) When a closed curve
isdisplayedattheCurvesub-objectlevel,the
initial CV is displayed as a green circle, and a
green tick mark indicates the curve’s direction.
Inter face
CV Curve rollout (cre ation time)
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. Default=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.
CV Curve rollo ut (modificatio n time)
Degree—Setsthedegreeofthecurve.Thehigher
the degree value, the greater the continuity. The
lowerthedegree,themorediscontinuousthe
cur ve segments become. The deg ree can’t b e less
than one or greater than the number allowed by
the number of CVs in t he 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