Circles in Perspective - Part Two

In Part One we learned the basics of how a circle in basic one point perspective becomes an ellipse.

 So how would another circle of the same size, say to the left of this one appear? Like this?:

That looks bigger than the center ellipse... maybe it should point to the vanishing point, like this:

Now that looks too small and really off...

In fact, in a perspective drawing like this, all ellipses on the ground plane will be oriented the same way - with their minor axes precisely vertical:

It might help if you think of each ellipse as the end of a cylinder. Since the sides of the cylinders are vertical, the ellipses are oriented vertically as well:

Interestingly, the same thing happens in two point perspective - as long as the sides of the (imaginary) cylinders are parallel, all the ellipses will be oriented the same way, in this case, vertically:

In Part Two we'll see how to apply this to a real drawing.