Function normalise_centroid 

pub fn normalise_centroid(
    centroid: &Vector3d,
    point: &Vector3d,
    pole: &Vector3d,
) -> Vector3d

Normalise a centroid on coincident great circles.

Note: it handles the case where the centroid is too small to normalise.

• centroid - the centroid to be normalised.
• point - a mid-point.
• pole - the pole of the Great Circle arc.

returns the normalise centroid.