The Spline tool in AutoCAD enables you to draw a smooth NURBS (Non-Uniform Rational B-Spline) curve that passes through or near a given set of points. Splines have been updated in AutoCAD 2011 to provide more flexibility and control than ever before.
You can access the Spline tool from various locations in the user interface including the Draw panel of both the 2D Drafting and Annotation workspace and the 3D modeling workspace. Since splines are particularly valuable for 3D surface modeling, you’ll also find the Spline tool in the Curves panel of the Surface ribbon tab.
When you begin drawing a spline, you can choose from two different methods: Fit (fit points) or CV (control vertices). The Fit method creates a spline that passes through the specified points whereas the CV method creates a spline that passes between the points.
Regardless of which method you chose when creating a spline, you can easily change the method of a selected spline in the Properties window. Or, better yet, change it directly on the object using the grip menu. Depending which method you choose, you’ll have different options for defining the spline.