Function calculate_reference_point_and_angle 

pub fn calculate_reference_point_and_angle(
    mid_point_0: &Vector3d,
    pole_0: &Vector3d,
    mid_point_1: &Vector3d,
    pole_1: &Vector3d,
) -> (Vector3d, Angle)

Determine the reference point of a pair of arcs. I.e. the closest intersection point if they intersect or the centroid normalized to lie on the unit sphere if they don’t.

• mid_point_0, mid_point_1 the mid points of the Arcs.
• pole_0, pole_1 the poles of the Arc great circles.

returns the closest intersection point or normalized centroid and the sine of the angle between the arcs, zero if the arcs are coincident. And the absolute relative angle at the intersection point or centroid.