Navigating effectively in virtual environments at human scales is a difficult problem. However, it is even more difficult to navigate in large-scale virtual environments such as those simulating the physical Universe; the huge spatial range of astronomical simulations and the dominance of empty space make it hard for users to acquire reliable spatial knowledge of astronomical contexts. This paper introduces a careful combination of navigation and visualization techniques to resolve the unique problems of large-scale real-time exploration in terms of travel and wayfinding. For large-scale travel, spatial scaling techniques and constrained navigation manifold methods are adapted to the large spatial scales of the virtual Universe. We facilitate large-scale wayfinding and context awareness using visual cues such as power-of-10 reference cubes, continuous exponential zooming into points of interest, and a scalable world-in-miniature (WIM) map. These methods enable more effective exploration and assist with accurate context-model building, thus leading to improved understanding of virtual worlds in the context of large-scale astronomy.
During the visualization of volume data, changing the illumination
condition provides us a way to reveal and emphasize the local structures within the volume. However, volume rendering with real-time lighting control is hard. It requires the re-computation of the amount of light received at each voxel after the attenuation, whenever the user changes the lighting condition. In this paper, we describe an image-based approach to relight (change the illumination) the volume in real time. The nature of image-based rendering decouples the rendering time complexity from the resolution of volume data. Hence, real-time relighting of volumetric data is possible even shadow (attenuation) is taken into account. Instead of re-computing all the lighting information, we pre-render (sample) a set of images (reference images) of the volumetric data under different illumination conditions. With these reference images, we are able to relight the volume under desired lighting condition by interpolating and superimposing pixel values. The relighting can be performed on ordinary PCs.
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