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Occlusion horizons for driving through urban scenery

We present a rapid occlusion culling algorithm specifically designed for urban environments. For each frame, an occlusion horizon is being built on-the-fly during a hierarchical front-to-back traversal of the scene. All conservatively hidden objects are culled, while all the occluding impostors of all conservatively visible objects are added to the 2½D occlusion horizon. Our framework also supports levels-of-detail (LOD) rendering by estimating the visible area of the projection of an object in order to select the appropriate LOD for each object. This algorithm requires no substantial preprocessing and no excessive storage. In a test scene of 10,000 buildings, the cull phase took 11 ms on a PentiumII 333 MHz and 45 ms on an SGI Octane per frame on average. In typical views, the occlusion horizon culled away 80-90% of the objects that were within the view frustum, giving a 10 times speedup over view frustum culling alone. Combining the occlusion horizon with LOD rendering gave a 17 times speedup on an SGI Octane, and 23 times on a PII. (Less)