Visualizing 3D atmospheric data with spherical volume texture on virtual globes

Volumetric ray-casting is a widely used algorithm in volume visualization, but implementing this algorithm to render atmospheric volume data that cover a large area on virtual globes constitutes a challenging problem. Because atmospheric data are usually georeferenced to a spherical coordinate system described by longitude, latitude and altitude, adaptations to the conventional volumetric ray-casting method are needed to accommodate spherical volume texture sampling. In this paper, we present a volumetric ray-casting framework to visualize atmospheric data that cover a broad but thin geographic area (because of the thinness of Earth׳s atmosphere). Volume texture conforming to the spherical coordinate system of a virtual globe can be created directly from the spherical volume data to avoid oversampling, undersampling or a loss of accuracy due to reprojecting and resampling such data into a Cartesian coordinate system. Considering the insignificant physical thickness of the atmosphere of the Earth, the ray-casting method presented in this paper also allows for real-time vertical scaling (exaggeration of the altitudinal range) without the need to re-process the volume texture, enabling convenient visual observation of the altitudinal variations. The spherical volume ray-casting method is implemented in a deferred rendering framework to integrate the volume effects into a virtual globe composed of a variety of background geospatial data objects, such as terrain, imagery, vector shapes and 3D geometric models.