Constructing Offset to Planar Bézier Curve by Cubic PH Curve

A given Bézier curve is subdivided into several segments by inserting knots. A cubic Pythagorean-Hogograph spline is constructed according to the conditions of endpoints and endpoint tangent vectors of each subdivision. This kind of PH-spline can be regarded as an approximation for the Bézier curve and its offset. The errors between Bézier curve and PH-spline, the offset to Bézier curve and the offset to PH-spline are also estimated.