A retroreflective BRDF model based on prismatic sheeting and microfacet theory

We propose a novel reflectance model for the physically based rendering of retroreflective materials, based on prismatic sheeting and microfacet theory. Due to its high performance, prismatic sheeting has been extensively used in material industry. We show through a geometric optics analysis that a prismatic sheet with a smooth incident plane exhibits perfect retroreflection, and retroreflectivity varies with respect to the incident direction. To permit imperfect retroreflection that appears frequently in many common situations, we model the incident plane as a rough surface with a microfacet profile. By adjusting surface roughness, we can easily change the angularity of the retroreflection lobe. We analyze thoroughly the relationship between surface roughness and glossiness of retroreflection using joint spherical warping strategy. Based on the analysis, a practical BRDF model is derived for materials with a prismatic sheet which comprises a surface reflection term, a retroreflection term, and a diffuse reflection term.