Photon mapping in image-based visual comfort assessments with BSDF models of high resolution

Abstract

Data-driven models replicate the irregular Bidirectional Scattering Distribution Functions (BSDFs) of optically Complex Fenestration Systems in daylight simulation. RADIANCE employs the tensor tree to store the BSDF at high directional resolution. Its application in backward ray-tracing is however challenging, since the density of stochastic samples must match the model resolution. BSDF proxy and peak extraction address this problem, but are limited to cases when either the fenestration geometry, or the shape and direction of the transmission peak are known. Photon Mapping is proposed to efficiently sample arbitrary BSDFs from the known sun direction. The existing implementation in RADIANCE is extended to account for light sources and their reflections in the field of view, that are of particular importance for visual comfort assessments. The method achieves a high degree of accordance with ray-tracing, and reduces simulation times by ≈95% with data-driven models of high resolution.Abbreviations: BRT: Backward Ray-Tracing; BSDF: Bidirectional Scattering Distribution Function; CBDM: Climate-Based Daylight Modelling; CFS: Complex Fenestration System; DGI: Daylight Glare Index; DGP: Daylight Glare Probability; FPM: Five Phase Method; GPGPU: General Purpose Graphics Processing Unit; LCP: Laser Cut Panel; OoC: Out-of-Core; PM: Photon Mapping; RMSE: Root Mean Squared Error