基于拒绝采样法的BRDF模型散射光线追迹方法  

Scattered Ray Tracing Method Based on BRDF Model by Rejection Sampling Method

作　　者：伦旭磊 朱丹[1] 高志山[1] 许宁晏 乔文佑 袁群[1] Lun Xulei;Zhu Dan;Gao Zhishan;Xu Ningyan;Qiao Wenyou;Yuan Qun(School of Electronic and Optical Engineering,Nanjing University of Science&Technology,Nanjing 210094,Jiangsu,China)

机构地区：[1]南京理工大学电子工程与光电技术学院,江苏南京210094

出　　处：《光学学报》2023年第6期210-217,共8页Acta Optica Sinica

基　　金：国家重点研发计划(2019YFB2005500);国家自然科学基金(62175107,U1931120);江苏省六大人才高峰项目(RJFW-019);中国科学院光学系统先进制造技术重点实验室基金(KLOMT190201);上海在线检测与控制技术重点实验室基金(ZX2021102)。

摘　　要：针对现有散射光线追迹概率模型方案受限于解析解难以获取的问题,提出利用拒绝采样法设计基于双向反射分布函数(BRDF)的散射光线追迹概率模型,通过设置检验条件规避了积分求解过程,进而筛选出有效角度坐标,实现散射光线追迹,该方案具有适用范围广的优势。对于具有平移不变性的BRDF模型,进一步提出对称采样方案,通过将采样区域减半后再镜像提升速率。设置表面属性、入射角与追迹光线数量等仿真条件相同,编制了本文方案的仿真程序,对不同光机结构材料进行建模仿真后从重复性和精确度方面与LightTools软件运算结果作对比验证,基于拒绝采样法编制程序的仿真结果可以与软件模型结果相媲美。最后对软件中未包含的BRDF模型进行建模仿真以进一步验证上述方案的普适性。Objective The bidirectional reflectance distribution function(BRDF)is commonly used to accurately characterize the scattering property of the surface of opto-mechanical structures in stray light analysis.Software for stray light analysis based on the Monte Carlo method(MCM)can construct probability models for scattered ray tracing on the basis of BRDF models.However,the types of BRDF models allowing surface property setting in the software are limited.Although the inverse transform technique can be used to construct probability models,the BRDF of most scattering models is modulated by multiple variables with complex forms,and the analytical solution of the cumulative distribution function is absent.Consequently,this method becomes invalid,and it also limits the application of BRDF models to some extent.As scattered ray tracing is limited by the difficulty in obtaining an analytical solution,a probability model for scattered ray tracing is constructed by the rejection sampling method.The proposed method circumvents the integral solution process by setting test conditions and then screens out the effective samples to achieve scattered ray tracing,whereby it gains the advantage of wide applicability.Methods The rejection sampling method is applied to construct the probability model for MCM-based scattered ray tracing in the present study.Specifically,the BRDF describing the scattering model is converted into a probability density function,and random sampling based on uniform distribution is performed.Then,a reasonable squeezing function is used,and the effective samples are screened out under the test conditions.Finally,the effective samples are taken as the direction of the scattered ray,and scattered ray tracing based on the BRDF model is thus achieved.For the shift-invariant BRDF model,a symmetric sampling scheme is further proposed to sample the half-space after determining the sampling interval.The angular coordinates are converted into direction cosines,and the effective samples are selected by the rejection s

关 键 词：测量 双向反射分布函数 光线追迹 拒绝采样法 蒙特卡罗法 概率模型 

分 类 号：TH741[机械工程—光学工程]