According to the nature of projective scale, it has solved the problem of drawing a cars perspective when perspective vanishing point is out of the drafting board.
文中利用射影几何中射线比的特殊性质，解决了透视灭点在图板外的透视图画法。
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The transformation from WCS to LCS can simplify the 3D drafting. The transformation from LCS to WCS can be used to generate the perspective projection.