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A personal annotations of Veach's thesis (7)

Here is my Japanese translation, part 3/3.

Robust Monte Carlo Methods for Light Transport Simulation
光輸送シミュレーションのためのロバストなモンテカルロ法

著者(Author): Eric Veach
Translated by Lx=d HY

1.1.2 輸送モデルに関する仮定

光輸送アルゴリズムは全ての光の振舞いをシミュレートするのではない．なぜなら，ほとんどの応用でそれは必要でないからである．(脚注: 厳密に言えばそれは可能ですらない．なぜなら全ての物理学が知られているわけではないからである．しかし，光と物体の相互作用は物理学の中でも最もよく研究され，発展しているものの一つである．そして実質的に全ての観測される現象は，かなり高い精度で計算，予測できる．[Feynman 1985] したがって，コンピュータグラフィックスの目的としては我々はこれらの物理法則は，ほぼ完全に理解されていると仮定してよい．) グラフィックスの立場に立つと，物理学における光学の知識を使うことは，写実的な画像を生成する手法として，最も適していると考えられる．どのようなシーンを生成するかに対して，我々はどの光学的効果が重要なのかを判断し，そしてそれをシミュレートできるアルゴリズムを選ぶことになる．

我々の論文においては幾何光学モデルを基礎とする．このモデルでは，光は物体の表面からのみ放射，拡散，吸収される．そして，これらの面間では光は直進すると仮定する．したがって，雲や煙のような participate 物体(吸収・拡散を行う物体)や，あるいは屈折率が連続的に変化する物体(たとえば，熱せられた気体)は考慮しない．我々はまた，波長や量子力学的効果に依存する(たとえば回折や蛍光)光学効果のほとんどを無視する．特に，我々は光線間の相互作用の可能性を排除する．すなわち，光は完全に非干渉であることを仮定する．

通常のレンダリングでは，ここで我々が無視した効果はそれほど重要ではない．幾何光学は我々が日常で目にするものをほとんど全て，適切に高い精度でモデル化する．このため，実質的には，ほとんどのグラフィックスでの光輸送アルゴリズムはここで行なった仮定と同様の仮定を行っている．この章の後ほどで，他の選択肢となる物理モデルの可能性に関して調査することにする(1.5 と 1.6 節参照)．
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