日光動態模擬的熱輻射法運算

Abstract

日光是最經濟且自然的光源，會隨著時間、地點、天氣狀況而動態改變能量大小，使得要以現有的熱輻射法模擬能量動態變化的日光並且做出隨著時間變化的動畫效果是一件困難的工作。我們提出以獨立光源為考量的熱輻射法來模擬日光動態變動的情形，利用單一光源能量變動時漸進式熱輻射法選擇場景發射多邊形順序不變的特性，針對環境中每一個光源分別獨立執行漸進式熱輻射法，並儲存所有多邊形的熱輻射和未發射熱輻射，顯像時再將每個光源儲存的個別多邊形熱輻射組合並成像。當時間改變時天空的能量隨之變化，我們的演算法可以保留場景的幾何資料，快速計算出天空能量變化後所有多邊形的熱輻射，不用重新再解熱輻射方程式，使得天空對地面場景隨著時間而變動的影響可以快速顯像。當使用者期望顯示某段時間內日光對場景的照射效果時，只需要設定起始、終止時間及模擬時間，我們的演算法可以在模擬時間內把場景在這段日光時間內所受到日光照射的情形模擬出來，展現出一段動畫效果。

Daylight is the most economical and natural light source, and will differ when the location of sun, time of the day, and the weather condition vary. Dynamically simulating daylight based on the traditional radiosity method and making it a smooth animation is no easy task. We propose an approach which treats light sources in the scene as independent as a sole light source in the progressive refinement radiosity (PRR) framework. By means of performing independent PRR computation for each luminaire with which stores the shot and unshot radiosity, the radiosity of polygons in the scene due to each luminaire can be linearly combined to achieve the final image as luminaires all have being functioning in the process of energy exchange. When changing the sky parameters or simulating the daylight, our proposed method can preserve geometry information of the scene, thus avoiding recomputing the radiosity from the scratch. Therefore, rapid rendering and displaying make daylight simulation with smooth animation possible. When the user expects to observe the daylight effects within a duration of time, he can only specify the starting and ending time of the simulation and the time slot for observation. Our proposed method can effectively simulate the daylight, while performing a vivid animation for observing the lighting variation.