8

1118 Chapter 9: Sur face Modeling
Procedure
ToturnaprimitiveintoaNURBSobject:
1.
Create the primitive object.
2. Go to the Modif y panel.
3. In the stack display, r ight-click the name of the
object.
4. Onthepop-upmenu,chooseConvertTo:
NURBS.
The object is converted to one or more CV
surfaces. The surfaces can be independent
surface sub-objects, or dependent surface
sub-objectssuchasLathe.
Nonr elati onal NU RB S S ur f aces
Select NURBS object. > Modify panel > General rollout >
Relational Stack toggle
Nonrelational NURBS surfaces provide a way
to improve the performance of NURBS with
modifiers. These are controlled by the Relational
Stack toggle on the General rollout for NURBS
objects.
When Relational Stack is on, NURBS maintain
full relational modeling on the
modifier stack
(page 3–802)
.Whenthistoggleisoff(thedefault),
then using the modifier st ack conve rts surfaces
int o independent CV surfaces before applying
modifiers. Surfaces on the stack behave in a
nonrelational w ay. If your NURBS model contains
no dependent surfaces, then it behaves the same on
the stack regardless of the Relational Stack setting.
However, the results are still faster if Relational
Stack is turned off.
When Relational Stack is off, there is no overhead
of copying the data from the relational model,
and no need to compute t he relational sur faces,
so performance is faster.
Tip: To improve performance still further, display
surfaces as shaded lattices (see
Display Controls for
NURBS Models (page 1–1119)
). With Relational
StackoffandShadedLatticechosen,NURBS
objectsperformonthestackaboutaswellasmesh
objects do.