This is a list of errata that some interested readers have found. (so far, it's only one bug, but several authors have complained about that one...). ----------------------------------------------------------- 1) hello Dr Wald, I think there is a small print error in the article "Realtime Ray Tracing and Interactive Global Illumination"; Chapter 7 Page 92: " H[u] = O[u] + t_plane * D[u]; H[v] = O[v] + t_plane * D[v]; " should be H[u] = O[u] + t_plane * D[u] - A[u]; H[v] = O[v] + t_plane * D[v] - A[v]; I tried it in my testing raytacer, It works, the original code not. :) Thank you! Baohe Zhang Shenzhen China