CSCW’00, December 2-6, 2000, Philadelphia, PA. ACM 1-58113-222-0/00/0012. Enabling Distributed Collaborative Science Tom Hudson1, Diane Sonnenwald2, Kelly Maglaughlin2, Mary Whitton1, and Ronald Bergquist2 1Department of Computer Science 2School of Information and Library Science University of North Carolina, Chapel Hill University of North Carolina, Chapel Hill Campus Box 3175, Sitterson Hall Campus Box 3360, Manning Hall Chapel Hill, NC 27599-3175 Chapel Hill, NC 27599-3360 {hudson, whitton}@cs.unc.edu {dhs, maglk, bergr}@ils.unc.edu

We present hierarchical occlusion maps (HOM) for visibility culling on complex models with high depth complexity. The culling algorithm uses an object space bounding volume hierarchy and a hierarchy of image space occlusion maps. Occlusion maps represent the aggregate of projections of the occluders onto the image plane. For each frame, the algorithm selects a small set of objects from the modelas occludersand renders them to form an initial occlusion map, from which a hierarchy of occlusion maps is built. The occlusion maps are used to cull away a portion of the model not visible from the current viewpoint. The algorithm is applicable to all models and makes no assumptions about the size, shape, or type of occluders. It supports approximate culling in which small holes in or among occluders can be ignored. The algorithm has been implemented on current graphics systems and has been applied to large models composed of hundreds of thousands of polygons. In practice, it achieves significant speedup in interactive walkthroughs of models with high depth complexity. CR

Computer Aided Design (CAD) and architectural models typically contain hundreds of thousands to millions of 3D primitives. In order to display these models at interactive rates, the number of primitives to be rendered must be reduced. This paper presents an experimental system which combines multiple simplification algorithms into a single framework for the rapid display of massive geometric models. We combine textured-box culling, levels-of-detail and occlusion culling into a single run-time system. We tested our framework on a 13 million triangles CAD model of a power plant and achieved highly interactive frame rates (speedups ranging from 50 to 100x) at the expense of some loss of image quality.