functions in rays.i - b

    best_rays(rays)  


returns 5-element (x,y,z,theta,phi) representation of RAYS.  
The first dimension of RAYS may be length 3, 5, or 6 to represent  
the ray(s) in TDG/DIRT coordinates (x,y,theta), "best" coordinates  
(x,y,z,theta,phi), or internal coordinates (cos,sin,y,z,x,r),  
respectively.  The first dimension of the result always has length 5.  
The "best" coordinate system is the easiest to visualize:  
(x,y,z) represents any point on the ray, while (theta,phi)  
represents the ray direction in standard spherical coordinates  
relative to the +z-axis.  Namely, theta is the angle from the  
+z-direction to the ray direction (between 0 and pi), and phi is  
the counterclockwise angle from the +x-axis to the projection of  
the ray direction into the xy-plane, assuming xyz is a right-handed  
coordinate system.  
As a specification of a ray, this system is doubly redundant because  
the point (x,y,z) could be any point on the ray, and the underlying  
mesh through which the ray propagates is cylindrically symmetric about  
the z-axis.  
However, the slimits parameter -- used to specify the points along  
a ray where the transport integration starts and stops -- is  
measured from the point (x,y,z) specified as a part of the  
(x,y,z,theta,phi) ray coordinate.  Thus, any change in the point  
(x,y,z) on a ray must be accompanied by a corresponding change in  
the slimits for that ray.  
Interpreted function, defined at i/rays.i   line 40