The quadrilateral in the right window represents the top-down projection of the perspective view, determined by the position of the viewpoint (EYE). Notice how any viewpoint on the semicircle passing through the two vanishing points (called viewing semicircle) always produces a rectangle.

Now let's construct the tiled floor to have something to reference against.

Now let's restrict the viewpoint to the viewing semicircle and let's try to keep the quadrilateral within the 60° cone of vision. Notice how the resulting perspective image is undistorted (in the sense that it resembles the top-down view, as shown in the right window).[br]