Landscapes Taking into Account Optical Effects of Clouds

Abstract

In this paper, we present a new method for representing optical effects caused by clouds, such as their shadows and illumination due to cloudy skylight, with practical precision. The proposed method is based on using a multi-layered parallelepiped for skylight illuminance, and allows us to calculate skylight luminance distribution with clouds located at arbitrary positions by efficiently obtaining a region of each cloud and its shadow volume. Traditional methods for rendering outdoor scenes considering skylight illuminance treat skylight luminance distribution for only perfectly clear or totally overcast weather, and ignore the effects of the distribution of clouds in the sky. Since a cloud is also usually defined as a density distribution model of participating media in voxels, we need much computation time for displaying a scene which renders dozens of clouds and their shadows. To solve these problems, we introduce “surface of a cloud” which consists of polygons, and use the depth information obtained by drawing them into depth buffers. Daytime landscapes under various weather conditions are rendered, and the results show the proposed method realizes a fairly satisfactory trade-off between computation time and quality of image including cloudy weather.