Smoothing an arc spline

Arc splines are G1 continuous curves made of circular arcs and straight-line segments. They have the advantages that the curvature of an arc spline is known and controlled at all but a finite number of points, and that the offset curve of an arc spline is another arc spline. Arc splines are used by computer-controlled machines as a natural curve along which to cut and are used by highway route planners as a natural curve along which to plan the centre line of a road. In this paper, it is shown how to increase the smoothness of a planar arc spline by replacing parts of it and thus to create a G2 continuous curve. The replacement parts are low-degree NURBS curves: cubic Bézier curves and quadratic rational Bézier curves.