To Extract User-Defined Spline Curves from Surfaces, Solids, and Faces of Solids

Use the Spline Points option to extract custom curves, not constrained in the U or V directions, from surfaces and solids.

1. Click Modify menu > 3D Operations > Extract Isolines.
2. Select a surface, solid, or face.
3. At the prompt, enter S to create a custom spline curve.

   Begin specifying points on the selected surface, solid, or face.

   As you click, a spline is created that passes through the specified points.

4. Press Enter to end the command.