Fast optical ray tracing using multiple DSPs

Optical ray tracing is a computationally intensive operation that is central both to the design of optical systems and to analyzing their performance once built. The authors have previously reported on the use of parallel digital signal processors (DSPs) to reduce the time required to perform ray tracing in analyzing the performance of the moderate resolution imaging spectroradiometer (MODIS), which is presently in orbit on multiple spacecraft. The earlier work was incomplete, providing only a conservative estimate of the performance improvement that could be achieved with one to four DSPs. This paper reports on the completed project and extends the earlier work to eight DSPs. As predicted in the earlier paper, not all rays make it through the entire optical system. Many are lost along the way. This is one factor that led to reduced processing time. Another is the use of an optimizing compiler. In this paper, the authors present results showing the separate effect of each of these two independent factors on the overall processing time. The most significant finding is the extraordinarily linear relationship between the number of DSPs available and the speed of the ray tracing. By using eight DSPs, the processing time is reduced from two weeks to less than one and a half days, an improvement of nearly a whole order of magnitude. Low-cost high-speed ray tracing is now feasible using off-the-shelf plug-in processor boards