Vanishing points need to be a long way away from the object you are drawing, otherwise you get some ridiculous effects. The closer the vanishing points are together, the closer your eye is to the object, so if you are drawing an object that is sitting on the table you are not normally going to look at it from a few centimetres away from it. So, vanishing points need to be away from the object, and in fact the best place for them is outside the page. The VP3 board does exactly this, in fact you will see that the vanishing points are even outside the drawing board itself. The centres of the arced slots are the vanishing points and when you put the tracking rule in one of the slots the lines you draw will automatically go to the vanishing point.
Three vanishing points?
In three-point perspective the two top vanishing points have something in common: they are on the same horizontal line, called the horizon line. This line represents the horizon. Everything above this line, you would look up to, and everything below this line you look down on. Most of the objects we would want to design are best viewed looking down on and for this reason the VP3 board has set the vanishing points this way.
What about the third vanishing point? This one is below the bottom of the page and is used for all vertical lines. It is placed a long way away, so the convergence effect is quite small, but it adds greatly to the realism of perspective drawing. In many books on perspective drawing they leave this vanishing point out because it is just too tricky to consider. But we live in three dimensions, so we should draw that way if we can too.
