By using the role and the drafting methods, projective contour line of a quadric at random position can be drawn.
利用这一规律和作图方法，可以解决任意位置的非退变二阶曲面的投影轮廓线的作图问题。
2
In this paper, a proper analytic methods is proposed for determining the projective formulas when their centers are improper points between two line pencils of projective correspondence.
This note shows that when studying geometric properties, a polynomial system is defined as a line field on a projective space such that its singular set has co dimension at least 2.