When a curve is tangent to another, I learned, when I was younger, that there are 2 possibilities for such tangent : a curve has 2 possible orientations, in a 3D affine space.
But SW designers haven't learn such basic concept.
So a relation of tangency give one choice, and get by with that....
I suggest that you spend your money with professional developments.
This begins with correct basic concepts with the affine geometry in affine spaces of dimension 3.
Message was edited by: Richard Doyle - Removed potential offensive word.