Function offset_chord_bound3 

pub fn offset_chord_bound3(
    curve: &Curve3,
    distance: Scalar,
    reference_direction: Vec3,
    a: Scalar,
    b: Scalar,
) -> Option<Scalar>

Certified chord bound of the offset of a 3D curve by distance along V x B' (see offset_point3) over [a, b] of the basis’s parameter; None as for offset_chord_bound2, or where the tangent may lie along V.