Function robust::orient3d

pub fn orient3d<T: Into<f64>>(
    pa: Coord3D<T>,
    pb: Coord3D<T>,
    pc: Coord3D<T>,
    pd: Coord3D<T>
) -> f64

Returns a positive value if the point pd lies below the plane passing through pa, pb, and pc (“below” is defined so that pa, pb, and pc appear in counterclockwise order when viewed from above the plane).
Returns a negative value if pd lies above the plane.
Returns 0 if they are coplanar.