Real-time simulation of sky and sun in clear day

Based on the atmospheric scattering principle, the paper summarizes the color and brightness characteristics of the Sun and sky in clear days at different time, and accordingly a real-time simulation to the characteristics is made in a day. We simulate the atmospheric Rayleigh scattering by sampling the gradients map and propose a simplified index formula to simulate the atmospheric Mie scattering. Furthermore, the high dynamic illumination of the Sun, sky and ground with auto-key high dynamic range lighting is taken into account in the simulation. The analysis to the experimental results shows that our system can achieve both real-time performance and high fidelity effects.