Bouatouch, Kadi2014-10-212014-10-2119881467-8659https://doi.org/10.1111/j.1467-8659.1988.tb00627.xSome theoretical extensions are brought to Koparkar and Mudur s method which deals with a polygonal approximation of parametric surfaces using potential extrema. The proposed extensions allow the determination of both the existence and the equation of a curve solution of potential extrema. Solutions are given to solve the crack problem and to avoid the artificats due to an inexact ray-surface intersection point near the silhouette or on the higher curvature regions. Moreover, two methods of ray tracing surfaces are proposed.10.1111/j.1467-8659.1988.tb00627.x257-264