It is shown that the 2_dimensional projective coordinate system can be constructed by homogeneous vector on the basis of the Descartes homogeneous coordinates.
在笛氏齐次坐标的基础上，采用齐次向量的方法，建立二维射影坐标系。
2
Two different surface straight lines distance not essential discovers male hangs the line segment, only must solve using the vectorprojective property then.