8

1240 Chapter 9: Sur face Modeling
CV sur faces. If Include Parent(s) is off, only the
one curve or surface is cloned. Cloning is slower
when Include Parent(s) is on, although quicker
than Relational Copy.
Select By Material ID Dialog
Modify panel > Select NURBS object. > Stack display >
Curve sub-object level > Select By ID button.
This dialog lets you select c urve sub-objects by the
material ID number assigned to them.
Inter face
ID—Specifies the material ID you want to select.
Clear S election—When on, replaces the current
selection (if any) by the material ID selection.
When off, adds the material ID selection to the
current select ion set.
Curve and Surface
Appr oximation
Curve Approximation
Modify panel > Select top-level NURBS object. > Cur ve
Approximation rollout
Although NURBS curves are analytically
generated, in order to generate and display them
they must be approximated by line seg ments.
Curve approximation controls are displayed in the
creation parameters for c urve objec ts, and on a
Curve Approximation rollout for NURBS models
(top-level NURBS objects). At the model level,
approximation controls affect all cur ve sub-objects
in the mo del.
Curve approximation is accomplished by
segments . One or more line segme nts, or steps,
areusedtoapproximateeachsegmentofthe
curve. For point curves, a segment of a curve is
the portion between one point and the next. For
CV curves, the segment is determined by the CV’s
parametric
knot (page 3–1055) .Thetransition
from one CV curve segment to another isn’t visible
in viewports.
Curve approximation parameters aren’t
animatable.
Interf ace
Steps—The maximum number of line segments
used to approximate each curve segment. If the
curve displays or renders with angles, increase this
value. This control is unavailable when Adaptive
is on. Range=1 to 100.
Optimi ze—Turn on this check box to opt imize the
curve. When on , interpolation uses the specified
Stepsvalueunlesstwosegmentsarecollinear,in
which case they are converted to a single seg ment.
This control is unavailable when Adaptive is on.
Adaptive—(The default.) Segments the curve
adaptively, based on its curvature. In other words,
the curve is assigned more segments where its