According to the concept of envelope evaluates equation of contour,the conclusion can be reached that the contour of torus is colse elliptc equidistant curve but is not ellipse.

• 根据包络的概念解出轮廓线的方程式,从而得出结论:圆环面的轮廓线是封闭的椭圆等距曲线,而不是椭圆。