Analytic ray-tracing formulas provide a rapid means of tracing rays, including skew rays, in a radial gradient. A fifth-order formula for the ray position and direction and a fourth-order formula for the optical path length give sufficiently accurate results for various applications.
© 1988 Optical Society of America
Erich W. Marchand, "Rapid ray tracing in radial gradients," Appl. Opt. 27, 465-467 (1988)