Figure 1. The N-Localizer and its Intersection with a Tomographic Section.
Side view of the N-localizer. A tomographic section intersects rods 
, 
, and 
. 
Tomographic image. The intersection of the tomographic section with rods 
, 
, and 
creates fiducial circles 
and 
and fiducial ellipse 
in the tomographic image. The distance 
between the centers of ellipse 
and circle 
and the distance 
between the centers of circles 
and 
are used to calculate the 
-coordinate of the point of intersection of the cylindrical axis of rod 
with the tomographic section [3].