Revolved surface orientation

How is the orientation of the surface determined by the revolve command? Is there a way to draw an open curve to ensure that revolving it will result in a specific orientation? I’m having trouble figuring this out by experimentation. Thanks.

You should be able to determine the orientation by comparing the curve’s starting tangent with the axis direction. If the dot product is positive, the normal should go to the left of the curve. I guess I probably need to explain what I mean by left. I’ll come up with something more precise.

Assuming the curve is planar, coplanar with the axis, does not cross the axis, and there is some point P on the curve but not on the axis, let Q be the closest point on the axis to P. Vector V = P-Q, Vector D = axis direction, T = curve starting tangent. (D x V) x T should be in the normal direction of the surface at the start of the curve.

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