THE FUTURE OF VIRTUAL GLOBES THE INTERACTIVE RAY-TRACED DIGITAL EARTH

摘要

In the past ten years graphics cards have been drastically improved. Being pushed by the multi-billion dollar computer game industry the capabilities and performance of graphics processors (GPUs) increased to support more and more geometric complexity and visual beauty in games. Today, virtual globes use similar techniques known from 3d-game programming, even though virtual globes use much more image data -which can be in the Petabyte range. Despite these architectural differences virtual globes are -like games -relying on a fast graphics card to maintain a high frame rate of 60 and more images per second at a high screen resolution. In the past decade there has also been an increase in CPU performance. With the advent of multi-core CPUs and algorithmic improvements it is now possible to reach acceptable interactive frame rates in ray-tracing using high-end multi-core PCs.Ray-tracing calculates an image by simulating the correct transport of light, obeying optical laws and energy conservation. Therefore ray-tracing allows for a substantial quality increase by supporting correct shadow calculation, depth-of-field, caustics, reflections, refractions, and so on. Global illumination adds much more realism to images. The problem of ray tracing is that a lot of computing power is required to create an image, especially for testing large amounts of intersections of light rays with the worlds geometry. There are ways to reduce computing power by using spatial acceleration structures. In the recent years those algorithms have been improved, so that interactive ray-tracing is now feasible. This paper shows how an interactively ray-traced virtual globe works. It shows how data preparation can be done, including acceleration structures for quick identification of spatial regions. A first implementation of such a physically correct digital earth is shown. Some possibilities with this system are presented and how the future of virtual globes looks like when this technology evolves.