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。

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.

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立体图指的是在观察图画中的深度时，通过双眼的配合能够构造出一幅心理上的立体透视图来。

A stereo view means that with cooperation of both eyes in perceiving depth from graphs, a single mental picture of perspective can be constructed.

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