A point on one line, its corresponding point on the other line, and the center of perspectivity are collinear.
一条直线上的一个点，它在另一条直线上的对应点以及透视中心这三个点共线。
2
A one-to-one correspondence between the points on two lines determined by a given point, not on either line, called the center of perspectivity or point of perspectivity.