Limitation:

The only limitation on the knots is that it is non-reducing.  The non- uniform rational B-spline of order J is then specified by

NURBS is one of most famous design curves in modern CAD. But as an instance, we shall consider the Rational quadratic curves-conic sections.

In this case

Along

ω(u) = (1 - u)²  ω₀ + 2u (1 - u) ω₁ + u ² ω₂

Therefore

lying in the convex hullof   is a plane curve. Also is a general quadratic; with appropriate choices of the vectorsand weights w_i , it might represent any conic segments exactly.

 Primary of all, if ω_i → k ω_i (k ≠ 0), C (u) remains the similar.