Geometric representation of the spherically-symmetric radiative transfer problem. The full radius mesh used for representing the variables as functions of radius is indicated along the radius vector by a set of concentric circles. The distance of rays from the stellar center is given by the impact parameter p. The set of rays that do not hit the core are represented by five parallel rays. The mesh of points used for solving the equation of radiative transfer are the crossing points between the circles and the horizontal lines. Distances along the rays are measured by z = μr where μ = cosθ.