学了
TracePro有一段时间了,一直没有注意到
重点采样这个功能,后来分析问题的时候发现
光线追迹的时间会因为光线数太多会达到30分钟甚至更多时间。了解有重点采样这个东西后,我直觉就是可以解决用相对较少的光线数来解决问题(直觉不科学,哈),所以就开始摸索。下面分享一下我的经验,我也有许多不会的,欢迎大家参加讨论。
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(j u-r*0 重点采样在User's Manual里面的描述是:
_QtqQ~f !^ 6x64r 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. M[_~7~4
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.
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h0-Dnw >TsJ0E?3x 自己尝试翻译一下为:
',0~ \V Cc]s94 重点采样是一种Monte Carlo技术,光线在光学系统里是按照特定的方向产生及传播的,这些方向在决定你需要的分析结果上面是非常重要的。重点采样通过增加到达用户感兴趣的表面的光线数来提高采样。重点采样在杂散光分析里是必要的,因为入射光的衰减可能很大,当然在其他的分析力也是很有用的。在杂散光分析里应该为光学系统里的每一个光学表面设定重点采样目标(improtant sampling target)。 o})4Jt1vj
要记住重点采样仅用来增强散射光,衍射光或者是表面光源的采样。在仅有镜面反射及透射的设计里不能利用重点采样,因为光线的传播的方向受反射定律及折射定律决定。 iQ-;0<