 
introduces a ray r
with source p and passing through point q.
 
 
introduces a ray r starting at source p with
direction d.
 
 
introduces a ray r starting at source p with
the direction of v.
 
 
introduces a ray r starting at source p with
the same direction as l.


 Test for equality: two rays are equal, iff they have the same source and the same direction.  

 Test for inequality.  

 returns the source of r.  


returns a point on r. point(0) is the source,
point(i), with i>0, is different from the
source.
 

 returns the direction of r.  

 returns a vector giving the direction of r.  

 returns the line supporting r which has the same direction.  

 returns the ray with the same source and the opposite direction. 

 ray r is degenerate, if the source and the second defining point fall together (that is if the direction is degenerate).  







 A point is on r, iff it is equal to the source of r, or if it is in the interior of r.  

 
checks if point p is on r. This function is faster
than function has_on() if the precondition
checking is disabled.


 
returns the ray obtained by applying t on the source and on the direction of r. 