This paper infers the parametric equation of the quadric B-spline curve, introduces its character, and gives the special method of process when the curve is approximated.
With the Lagrange multiplier method, the minimum distance of the center of a circle and a quadric surface was provided and the tangency condition of curve and surface was given.
利用拉格朗日乘子法求解二次曲线和二次曲面之间的最小距离，给出了曲线与曲面相切的条件。
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Furthermore, the subdivision formula of the quadric C-curve is presented at its arbitrary point.