Function lune_classify 

pub fn lune_classify(
    a: &SphericalPoint,
    b: &SphericalPoint,
    point: &SphericalPoint,
) -> LuneSide

Determines which side of the angular bisector plane between a and b a point lies on.

The bisector plane is defined by the great circle equidistant from a and b. Points on A’s side are angularly closer to A than to B.