Yes, that's fine - although while I vaguely remember a technique using a compass, I feel like what it produced wasn't actually an ellipse (although that isn't inherently a problem in and of itself, as the ellipses themselves are technically very useful approximations of what a circle projected into 2D would look like, which holds quite well in most cases but breaks down in more extreme 3 point perspective). If you have a link for the technique, I'd certainly like to take a look.