8

NURBS and Modifiers 1091
NUR B S a nd M odif ier s
In general, you can apply modifiers to NURBS
modelsasyoudotootherobjects.
Yo u c a n a p p l y
Edit Patch (page 1–617) and Edit
Mesh (p age 1–613)
modifiers to NURBS surface
objects.
Tip: Toimproveperformancewhileyouanimate
your scene, make the surfaces in your NURBS
model
nonrelational surfaces (page 1–1118) .
Modifierstreatnonrelationalsurfacesasifthey
were independent CV sur faces: you can animate
the scene more efficiently, and then turn relational
modeling back on before you render.
Deforming NURB S Objects
Deform modifiers such as Bend (page 1–541)
and Tw ist (page 1–865) operate on CV and point
sub-objects. They don’t change the NURBS model
into an editable mesh object. This means that
youcanuseadeformmodifier,collapsethestack,
and still have a NURBS object that you can edit
further. However, because the deform modifiers
directly affect CVs and points (and not the mesh
approximation of the NURBS model), they can
produce unexpected results. For example, a
Ripple
(page 1–773)
modifier does not ripple the surface
if the CVs are far ther apart than the wavelength
of the ripples. If you want the modifier to affect
the mesh approximation instead of the CVs, you
can apply a
Mesh Select (page 1–710) modifier
first. Then when you collapse t he stack, you get an
editable mesh, not a NURBS object.
These are the deform modifiers that collapse to
NURBS:
• Modifiers in the Parametric Modifiers set,
except for Lattice (which collapses to an
editable mesh) and Slice (which collapses to an
editable poly or an editable mesh).
• Modifiers in the Animation Modifiers set,
except for the world space modifier versions of
PatchDeform, PathDeform, and SurfDeform
(which don’t collapse).
Tip: While they w ill collapse to a NURBS object,
the Morpher and Skin modifiers are meant to
be used with their own controls, and lose their
usefulness when you collapse them.
The modifiers with Sof t Selection controls treat
NURBSmodelsthesamewaytheytreateditable
meshes. As with editable mesh vertices, CVs are
colored proportionally according to how severely
the region affects them.
If Relational Stack is turned off (see
Nonrelational
NURBS Surfaces (page 1–1118)
), the Affect
Neighbors toggle can affect all surface CVs, curve
CVs, and points in neighboring sub-objects.
If Relational Stack is on, Soft Selection affects
neighboring sub-objects only if they are at the
same sub-object level.
Soft Selection works with Scale and Rotate as well
as w ith the Move transform.
NURBS Objects and the UV W Map
Modifier
When you apply a UVW Map (page 1–905)
modifier, it affects the NURBS object the same way
it affec ts a mesh. If you then collapse the stack,
UVW mapping is still in effect. However, you
can override the mapper for individual surface
sub-objects. Todoso,turnonthesurface’s
Generate Mapping Co ords check box, if necessary.
When the check box is on, you get the natural
mapping of the surface; when it is off, you get the
mapping from t he collapsed UVW modifier.
Tip: Don’t use UVW Map to assign a texture to
an animated surface. The texture w i ll shift as the
surface animates.