Katsumi Tadamura Xueying Qin Guofang Jiao Eihachiro Nakamae Rendering optimal solar shadows with plural sunlight depth buffers. 76-90 2001 17 The Visual Computer 2 http://link.springer.de/link/service/journals/00371/bibs/1017002/10170076.htm db/journals/vc/vc17.html#TadamuraQJN01