Function find_tangent_contact 

pub fn find_tangent_contact(
    first: &NurbsSurface,
    second: &NurbsSurface,
    tolerance: f64,
) -> Result<Option<TangentContact>, String>

Find a tangential contact between two carriers without a witness: grid the first carrier, project each sample onto the second, rank the samples by their distance and the angle between the normals, and refine the best few onto the contact. The grid is then repeated from the second carrier, so a contact one carrier samples poorly is still reached from the other.

None means no sample refines onto a contact — the carriers do not touch tangentially anywhere the grids see.