One of the fundamental problems with direct manipulation in a 2D projection of a 3D scene is the problem of translating 2D motions of the cursor in the plane of the screen into a more meaningful movement in the virtual 3D space.

• 三维场面的二维投影中，使用直接操作的基本问题之一就是如何将屏幕上光标的二维移动转换为虚拟三维空间内更有意义的移动。