An Analytic Model for Full Spectral Sky-Dome Radiance

Abstract

We present a physically-based analytical model of the daytime sky. Based on the results of a first-principles brute force simulation of radiative transfer in the atmosphere, we use the same general approach of fitting basis function coefficients to radiance data as the Perez and Preetham models do. However, we make several modifications to this process, which together significantly improve the rendition of sunsets and high atmospheric turbidity setups — known weak points of the Preetham model. Additionally, our model accounts for ground albedo, and handles each spectral component independently. The latter property makes it easily extensible to the near ultraviolet range of the spectrum, so that the daylight appearance of surfaces that include optical brighteners can be properly predicted. Due to its similar mathematical properties, the new model can be used as a drop-in replacement of the Preetham model.

Note: to access the paper PDF and the model source code, please use the “Source Code” link on your right. This leads you to the old sky dome modelling project page of our group, where these are provided (please scroll to the bottom, there are two other publications presented on that page). Lots of people have links to the old page, so we are leaving this as it is.

Please also note that our 2021 SIGGRAPH paper on sky dome modelling provides a much improved sky model that is also available for download! Unless compatibility with old codebases is essential, the new model should be used whenever possible!

BibTex Citation

				
					An Analytic Model for Full Spectral Sky-Dome Radiance