CGAL 5.6.1  2D and 3D Linear Geometry Kernel

AdaptableUnaryFunction
Operations  
Kernel::Vector_3  operator() (const Kernel::Plane_3 &p) 
returns a vector that is orthogonal to the plane p and directed to the positive side of p .  
Kernel::Vector_3  operator() (const Kernel::Point_3 &p, const Kernel::Point_3 &q, const Kernel::Point_3 &r) 
returns a vector that is orthogonal to the plane defined by Kernel::ConstructPlane_3()(p, q, r) and directed to the positive side of this plane.  