Like the Shape object, a NURBS model can be an assemblage of multiple NURBS sub-objects. For example, a NURBS object might contain two surfaces that are separate in space. You control NURBS curves and NURBS surfaces with point or control vertex (CV) sub-objects. Points and CVs behave somewhat like the vertices of spline objects, but there are differences.
The parent object in a NURBS model is either a NURBS surface or a NURBS curve. Sub-objects can be any of the objects listed here. A NURBS curve remains a Shape object unless you add a surface sub-object to it when you convert it to a NURBS surface (without changing its name).
There are two kinds of NURBS surfaces. A point surface is controlled by points, which always lie on the surface. A CV surface is controlled by control vertices (CVs). Instead of lying on the surface, CVs form a control lattice that surrounds the surface. (This is similar to the lattice used by the FFD [free-form deformation] modifiers.)
See Creating Surface Sub-Objects and Editing Surface Sub-Objects.
There are also two kinds of NURBS curves. These correspond exactly to the two kinds of surfaces. A point curve is controlled by points, which always lie on the curve. A CV curveis controlled by CVs, which don't necessarily lie on the curve.
See Creating Surface Sub-Objects and Editing Curve Sub-Objects.
Point surfaces and point curves have point sub-objects. You can also create separate point sub-objects that are not part of a surface or a curve.
CV surfaces and CV curves have CV sub-objects. Unlike points, CVs are always part of a surface or a curve.
See Editing Curve CV Sub-Objects and Editing Surface CV Sub-Objects.
Imports are 3ds Max objects, including other NURBS objects. Within the NURBS model, they render as NURBS; but they retain their original parameters and modifiers.
See Attaching and Importing 3ds Max Objects.
Sub-objects can be dependent sub-objects whose geometry is related to the geometry of other sub-objects.
To create a NURBS model, use one of the methods described here.
When you work with NURBS models, usually you create one NURBS object as the “starter” object, then edit the starter object or add additional sub-objects.
To trim a surface is to use a curve on the surface to cut away part of the surface, or to cut a hole in the surface.
You can edit NURBS immediately when you enter the Modify panel. There’s no need to apply a modifier, as with some other kinds of 3ds Max objects.
While a NURBS object is selected and the Modify panel is active, the quad menu displays two quadrants that are specifically for NURBS editing.
Besides using rollouts at the NURBS object level, you can use the NURBS toolbox to create sub-objects.
When you work with NURBS models, you often work with sub-objects. While you are at the sub-object level, you use the usual selection techniques, such as clicking, dragging a region, or holding down Ctrl, to choose one or more sub-objects.
Independent curves and independent surfaces both come in two varieties: they are either CV sub-objects or point sub-objects. This topic describes the differences between the two.
A NURBS sub-object is either independent or dependent. A dependent sub-object is based on the geometry of other sub-objects. For example, a blend surface smoothly connects two other surfaces. Transforming or animating either of the original, parent surfaces causes the shape of the blend to change as it maintains a connection between the parents.
To improve performance, you can make any kind of surface sub-object into a rigid surface. The only editing allowed on a rigid surface is to transform it at the Surface sub-object level. You can't move a rigid surface's points or CVs, or change the number of points or CVs.
In general, you can apply modifiers to NURBS models as you do to other objects.
In general, you animate NURBS curves and NURBS surfaces by turning on the Auto Key button and transforming sub-object attributes such as CV or point positions, by animating the parameters that control dependent NURBS objects, and so on.
NURBS curves and surfaces did not exist in the traditional drafting world. They were created specifically for 3D modeling using computers. Curves and surfaces represent contours or shapes within a 3D modeling space. They are constructed mathematically.
These topics contain suggestions on how to work with NURBS. They include tips collected from various NURBS modeling users.
