[原創(chuàng)]TracePro中的重點采樣 [復制鏈接]

Importance sampling is a Monte Carlo technique in which rays are generated and propagated in specific directions in the optical system, which are “important” in determining the results you need. This improves sampling by increasing the number of rays reaching the surface or surfaces of interest to the user. Importance sampling is essential in a stray light analysis, where the attenuation of incident light can be very great, and can be helpful in other types of analyses. In a stray light analysis, there should be an importance sampling target for each optical surface in the optical system. It is important to remember that importance sampling is used only to enhance the sampling of scattered and diffracted light or surface sources. Designs that include only specular reflection and transmission cannot take advantage of importance sampling — the direction of the rays is determined by the Law of Reflection and Snell’s Law. ;|:R*(2   
Figure 7.1 on page 7.3 illustrates importance sampling for the simple case of a lens that scatters from its second surface. A second object is shown that corresponds to a detector. In this case rays from an off-axis field position are imaged such that all of the specular rays miss the detector. Generally, scattering is stronger close to the specular direction of the un-scattered ray so the probability of a randomly scattered ray hitting the detector is very small. When an importance target is applied, it guarantees that the one or more importance rays will hit the detector for each incident ray.

重點采樣是一種Monte Carlo技術，光線在光學系統(tǒng)里是按照特定的方向產生及傳播的，這些方向在決定你需要的分析結果上面是非常重要的。重點采樣通過增加到達用戶感興趣的表面的光線數來提高采樣。重點采樣在雜散光分析里是必要的，因為入射光的衰減可能很大，當然在其他的分析力也是很有用的。在雜散光分析里應該為光學系統(tǒng)里的每一個光學表面設定重點采樣目標(improtant sampling target)。 8 VhU)fY  
要記住重點采樣僅用來增強散射光，衍射光或者是表面光源的采樣。在僅有鏡面反射及透射的設計里不能利用重點采樣，因為光線的傳播的方向受反射定律及折射定律決定。 NFR>[L V  
在7.3頁的圖7.1展示的是對在它自己的第二個表面散射的鏡頭的重點采樣的簡單例子。第二個物體是相對應的探測器在這個例子里，遠離光軸的光纖成像以至于所有的鏡面反射光都沒有到達探測面。通常來說在靠近 沒有散射的光線的 反射方向上散射會更強一點，所以隨機散射的光到達探測器的可能性就很小。一旦我們應用了重點采樣目標，對于每一個入射光會有更多的重點采樣光線到達探測器。