Direction_3<Kernel> d ( Vector_3<Kernel> v);  
introduces a direction d initialized with the
direction of vector v.
 
Direction_3<Kernel> d ( Line_3<Kernel> l);  
introduces the direction d of line l.
 
Direction_3<Kernel> d ( Ray_3<Kernel> r);  
introduces the direction d of ray r.
 
Direction_3<Kernel> d ( Segment_3<Kernel> s);  
introduces the direction d of segment s.
 
Direction_3<Kernel> d ( Kernel::RT x, Kernel::RT y, Kernel::RT z);  
introduces a direction d initialized with the direction
from the origin to the point with Cartesian coordinates (x, y, z).

Kernel::RT  d.delta ( int i) const 
returns values, such that d== Direction_3<Kernel>(delta(0),delta(1),delta(2)).
 
Kernel::RT  d.dx () const  returns delta(0).  
Kernel::RT  d.dy () const  returns delta(1).  
Kernel::RT  d.dz () const  returns delta(2).  
bool  d.operator== ( e) const  Test for equality.  
bool  d.operator!= ( e) const  Test for inequality.  
Direction_3<Kernel>  d.operator () const  The direction opposite to d.  
Vector_3<Kernel>  d.vector () const  returns a vector that has the same direction as d.  
Direction_3<Kernel>  d.transform ( Aff_transformation_3<Kernel> t) const  
returns the direction obtained by applying t on d. 