A NURB is a **N**on-**U**niform, **R**ational, **B**-spline. It is a mathematical technique using polynomials to describe smooth curves or surfaces. The ‘**B**’ stands for “Basis”. It was developed in the early 1970’s as a method for creating smooth curves and surfaces interactively on the computer screen. A NURB is defined using **vertex points**, a **knot vector**, a **polynomial degree**, and one **weight value** per vertex point. The most identifying feature of a NURB is that the curve (or surface) does not pass through the defining vertex points. This means that a program that uses NURBs allows you to edit the shape of a curve or surface by moving or dragging these vertex points. Since these vertex points do not lie on the curve or surface, the program usually connects the vertex (edit) points with straight lines. These lines are sometimes called the vertex mesh for NURB surfaces.

To avoid the screen clutter of the vertex lines or mesh and to make the job of directly controlling curve and surface shape, Pilot3D allows you to edit the shape using points that lie on the curve or surface.

For a detailed discussion of NURBS and all of their options, see the white paper called “The Dirty Little Secrets of NURBs”.