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
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
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