Tips for constructing NURBS curves

Create simple curves

Use the simplest curves that can describe the shape you want. This means construct curves with the least amount of CVs or edit points possible. Simpler curves mean simple, faster rendering surfaces.

One effective method for achieving simple curves is:

1. Begin a curve by drawing a single span.
2. Move the interior CVs on the curve to achieve the shape you want.
3. If you can’t achieve the shape you want, add an interior edit point to create more CVs.
4. Continue this process until you have the curve shape you need.

This iterative process ensures your curve only has as many spans as are absolutely necessary.

You can also use the Rebuild curve tool to simplify existing curves. The tool can simplify a curve while maintaining its shape within a tolerance you set.

Note the curve’s parameterization

It is often best to build curves with uniform parameterization, because it makes inserting edit points and detaching curves at exact locations easier.

• When drawing Edit point curves with Uniform parameterization, the resulting CVs may be placed awkwardly. To fix this, move the CVs to prevent crossing hull lines.
• Try to consistently use either Uniform or Chord length parameterization when drawing curves. If you mix and match curve styles, it could result in cross knot insertion when the curves are used to build a surface.

Plan your surfaces in advance

When creating curve, plan ahead to the surfaces that you want. Try to have the same number of spans in all the construction curves for building a surface. A simple way to achieve this is to start with one curve, then duplicate it to create more construction curves.

When you create a surface from curves with different numbers of spans, the new surface will have an extra isoparametric curve corresponding to every extra edit point. This is known as cross knot insertion. It makes the new surface more difficult to edit and more complex.