Editing Fit and Spline Polylines

AutoCAD recognizes both fit polylines and spline-fit polylines. A spline-fit polyline uses a curve fit, similar to a B-spline. There are two kinds of spline-fit polylines, quadratic and cubic. Both of these polylines are controlled by the SPLINETYPE system variable. A fit polyline uses standard curves for curve fit and utilizes any tangent directions set on any given vertex. You can change the splined polyline back to a polyline using the Decurve option.

The illustration shows a polyline edited with the Spline option.

However, some editing actions, such as trimming, breaking, and any grip editing, remove the spline definition of a fit or splined polyline. For this reason, it is better to use a true spline, which maintains its spline definition.