Adding a Solar-Radiance Function to the Hošek-Wilkie Skylight Model

One prerequisite for realistic renderings of outdoor scenes is the proper capturing of the sky´s appearance. Currently, an explicit simulation of light scattering in the atmosphere isn´t computationally feasible, and won´t be in the foreseeable future. Captured luminance patterns have proven their usefulness in practice but can´t meet all user needs. To fill this capability gap, computer graphics technology has employed analytical models of sky-dome luminance patterns for more than two decades. For technical reasons, such models deal with only the sky dome´s appearance, though, and exclude the solar disc. The widely used model proposed by Arcot Preetham and colleagues employed a separately derived analytical formula for adding a solar emitter of suitable radiant intensity. Although this yields reasonable results, the formula is derived in a manner that doesn´t exactly match the conditions in their sky-dome model. But the more sophisticated a skylight model is and the more subtly it can represent different conditions, the more the solar radiance should exactly match the skylight´s conditions. Toward that end, researchers propose a solar-radiance function that exactly matches a recently published high-quality analytical skylight model.