9

1116 Chapter 9: Surface Modeling
Cr e a t in g NU RBS S u rfaces fro m
Geometric Primitives
Primitive objects become NURBS surfaces that you can then
edit in various ways.
Yo u c a n t u r n a standard primitive (page 1–170)
into a NURBS object formed of CV surfaces (page
1–1179). Once converted, you can no longer edit
theobjectparametrically,butyoucanedititasa
NURBS object, moving CVs and so on.
Youcan’tconvertmostextendedprimitiveobjects
in this way, but you can convert the torus knot
(page 1–189) and prism (page 1–205) extended
primitives to NURBS objects.
Yo u c a n a l s o c o n v e r t patch (page 1–993) objects
and loft (page 1–352) compound objects.
Tips
• Geospheres are good for creating rounded
models with no sharp edges.
• Boxes are good for creating models that have
sharp edges.
• Flattened cones work well for models whose
contours are roughly triangular.
If the primitive is closed, the conver ted surface is
a closed CV surface, which has no visible seams.
Also, relat ional cap surfaces (page 1–1195) are u sed
tocapsurfacesthataren’tclosed.
Procedure
To turn a pr imitive into a NUR B S object:
1.
Create the primitive object.
2. Go to the Modify panel.
3. In the stack display, r ig ht-click the name of the
object.
4. On the pop-up m enu, choose Convert To:
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 NUR B S S urfa ces
Select NURBS object. > Modify p anel > General rollout >
Relational Stack toggle
Nonrelational NURBS surfaces provide a way
to improve the performance of NURBS with
modifiers. T h ese are controlled by the Relational
Stack toggle on the General rollout for NURBS
objects.