NURBS and Modifiers

In general, you can apply modifiers to NURBS models as you do to other objects.

You can apply Edit Patch and Edit Mesh modifiers to NURBS surface objects.

Tip: To improve performance while you animate your scene, make the surfaces in your NURBS model nonrelational surfaces. Modifiers treat nonrelational surfaces as if they were independent CV surfaces: you can animate the scene more efficiently, and then turn relational modeling back on before you render.

Deforming NURBS Objects

Deform modifiers such as Bend and Twist operate on CV and point sub-objects. They don't change the NURBS model into an editable mesh object. This means that you can use a deform modifier, collapse the stack, 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 modifier does not ripple the surface if the CVs are farther 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 modifier first. Then when you collapse the stack, you get an editable mesh, not a NURBS object.

These are the deform modifiers that collapse to NURBS:

• Modifiers in the Parametric Deformers 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 (WSM) versions of PatchDeform, PathDeform, and SurfDeform, which don't collapse.

Tip: While the Morpher and Skin modifiers collapse to a NURBS object, they are meant to be used with their own controls, and lose their usefulness when you collapse them.

The modifiers with Soft Selection controls treat NURBS models the same way they treat editable meshes. As with editable mesh vertices, CVs are colored proportionally according to how much the region affects them.

If Relational Stack is turned off (see Nonrelational NURBS Surfaces), 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 with the Move transform.

NURBS Objects and the UVW Map Modifier

When you apply a UVW Map modifier, it affects the NURBS object the same way it affects 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. To do so, turn on the surface's Generate Mapping Coords checkbox, if necessary. When the checkbox is on, you get the natural mapping of the surface; when it is off, you get the mapping from the collapsed UVW modifier.

Tip: Don't use UVW Map to assign a texture to an animated surface. The texture will shift as the surface animates.

NURBS Surface Select Modifier

The Surface Select modifier lets you place a NURBS sub-object selection on the modifier stack. This lets you modify only the selected sub-objects. Also, selected curve sub-objects are Shape objects that you can use as paths and motion trajectories.

Surface Select can select any kind of NURBS sub-object except imports. Each sub-object selection is of one sub-object level only.

Procedures

To use the Surface Select modifier:

1. With a NURBS object selected, go to the Modify panel and apply Surface Select.

   The modifier has no controls at the object level.

2. Click to open the modifier's hierarchy, and choose a sub-object level.

   The selection modifier has the same selection controls you see for the corresponding sub-object type.

   While applying the modifier, you can also select NURBS sub-objects by name. Turn on the Keyboard Shortcut Override Toggle and then press the H key. This open the Select Sub-Objects dialog, which is a subset of the Selection Floater that you can use during sub-object creation as well as sub-object selection. Choose one or more objects in the list, and then click Select. Press +H to have the Select Sub-Objects dialog list only sub-objects (for example, points) directly under the mouse cursor.

3. Use the selection controls to create a selection set of the chosen sub-object type.

   With the Surface Select modifier, you can select NURBS sub-objects at any level except imports.

Note: To select point, curve, or curve CV sub-objects, you must go to the NURBS object and turn on Relational Stack.

Once you have used the modifier to create the selection, you can apply other modifiers to it. If the selected sub-object is a curve, you can also use it as a path or trajectory.

Note: Surface Select doesn't support copying and pasting of selections as Mesh Select does. Copying and pasting mesh selections is based on vertex indexes. NURBS selections are based on object IDs, which are unique to each model.