(a) L R s (u; s) C i (u) (b) L R s (u; s) C i (u) Figure 9: A direct intersection curve tracing of a DSSI between a developable surface R s (u; s) and the Utah teapot, is used to derive the domain of C i (u) that is in shadow. Two views of the same scene are provides. a tight link between two diicult problems from the two elds of computer graphics and computer aided geometric design, namely SSI and RSI. One can consider the ruled tracing method that manipulates bivariate surfaces as an intermediate approach between the trivariate wavefront paradigm of 11] and the univariate ray tracing methods. It is possible that the ruled tracing method might be used as an optimization tool for contemporary ray tracing techniques. Time comparisons are essential for the evaluation of this possibility, a comparison that must be made by incorporating this method into an existing ray tracer while optimizing the SSI algorithm to the case herein, namely R/DSSI. We are currently working on such an implementation. Freeform surfaces can now be directly scan converted and ray/ruled traced. The emulation of diiuse lighting via methods such as Radiosity is yet to be solved. Combining the Radiosity and ray/ruled tracing techniques, as in 13], should also be considered.