This is just not the case. You can have three orthogonal vanishing points all inside the bounds of an image and it can look just fine. It just corresponds to ha

This is just not the case. You can have three orthogonal vanishing points all inside the bounds of an image and it can look just fine. It just corresponds to having a field of view wider than 90 degrees (which looks a bit unnatural but can be a dramatic way of presenting an image). Imagine standing on the corner of a city block, such that without turning your head you can look down both streets and up at the sky. You can see the two streets recede off into the distance and the skyscraper above you foreshorten towards a vanishing point far overhead. Of course a vanishing point can be inside a perspective drawing, after all where do you put the vanishing point for one-point perspective?