## functions in rays.i - b

best_rays
```
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

```