 
introduces a direction d initialized with the
direction of vector v.
 
 
introduces the direction d of line l.
 
 
introduces the direction d of ray r.
 
 
introduces the direction d of segment s.
 
 
introduces a direction d initialized with the direction
from the origin to the point with Cartesian coordinates (x, y, z).



returns values, such that d== Direction_3<Kernel>(delta(0),delta(1),delta(2)).
 

 returns delta(0).  

 returns delta(1).  

 returns delta(2).  

 Test for equality.  

 Test for inequality.  

 The direction opposite to d.  

 returns a vector that has the same direction as d.  

 
returns the direction obtained by applying t on d. 