Editing Autodesk 3ds Max (section)

=== NURBS (Non-Uniform Rational Based-Splines) ===
An alternative to polygons, it gives a smoothed out surface that eliminates the straight edges of a polygon model. [[NURBS]] is a mathematically exact representation of freeform surfaces like those used for car bodies and ship hulls, which can be exactly reproduced at any resolution whenever needed. With NURBS, a smooth sphere can be created with only one face.

The non-uniform property of NURBS brings up an important point. Because they are generated mathematically, NURBS objects have a parameter space in addition to the 3D geometric space in which they are displayed. Specifically, an array of values called knots specifies the extent of influence of each control vertex (CV) on the curve or surface. Knots are invisible in 3D space and can't be manipulated directly, but occasionally their behavior affects the visible appearance of the NURBS object. Parameter space is one-dimensional for curves, which have only a single U dimension topologically, even though they exist geometrically in 3D space. Surfaces have two dimensions in parameter space, called U and V.<ref>[http://www.rw-designer.com/NURBS "NURBS Curves and Surfaces"], November 22, 2013</ref>

NURBS curves and surfaces have the important properties of not changing under the standard geometric affine transformations (Transforms), or under perspective projections. The CVs have local control of the object: moving a CV or changing its weight does not affect any part of the object beyond the neighboring CVs. (This property can be overridden by using the Soft Selection controls). Also, the control lattice that connects CVs surrounds the surface. This is known as the convex hull property.<ref>{{cite web |url=https://math.stackexchange.com/q/118937 |title=Why is the Convex Hull property so important |date=November 22, 2013 |work=Stack Exchange }}</ref>