The double circle-arc fitting in the same direction and in the opposite direction are given in the original coordinates for arbitrary plane parametric curves, after the straight line, the circular-arc, the parametric curve and its tangent line are oriented. The circular-arc fittings for plane curve of tabular points are discribed by using the cubic spline function. Newton method is used to calculate the maximum error and the result of high precision has been gained by densifying points. The advantage of the method is that if overcomes difficulties of large defiection, high precision, huge programming, and avoid solving the nonlinear equations.
