A visualization framework for cloud rendering in global 3D GIS

Clouds are integral part in 3D-GIS visualization, without them 3D scene seem unrealistic. The paper presents a technical framework to simulate clouds from macroscopic to microcosmic scale in Global 3D-GIS. In the case of the macroscopic scale, which means the viewpoint is far away from the 3D scene in 3D-GIS, cloud was expressed with semi-transparent planar texture. In other case, we consider the cloud as a collection of particles collecting light from the sun, and the 3D-cloud is indexed with octree and modeled with particle system. The scattering light model and billboard technique are used to render it. Meanwhile, this article proposed a cloud visualization scheduling algorithm based on viewpoint position, aiming at the smooth switching between the 2D and 3D cloud. The technical framework supports numerous clouds to be rendered at high stable frame rates, and has been embedded into ChinaStar, a global 3D-GIS platform manufactured by the authors.