It is defined that a curve is positively oriented if when one travels along it, the region enclosed by the curve is to his left. But if this curve exists in 3D, and one goes to the other side of the curve, and travels along the same direction, then the curve will be to his left! So isn't this definition ambiguous? (I attached a simple sketch of this to make my point clearer.) How can you specify which way to go around a curve unambiguously? "Clockwise" and "anticlockwise" depends from where you're looking at the curve, and so does this "region to your right/region to your left" business.