How can I know if the TOROIDAL_SURFACE in STEP file represents a concave or a convex curve?

Any TOROIDAL_SURFACE has four circles. Each circle is represented by: radius, start point (x, y, z), end point (x, y ,z), center point (x, y, z), and two lines of direction of the center point.
1-How can I know if the TOROIDAL_SURFACE represents a concave or a convex? because both of the cases are possible.
2- Can anyone please give an explanation about the (two lines of direction) with an example? I don't understand the concept of these direction.

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