Study On Visibility Culling In Virtual Reality Engine

Virtual Reality technology has developed rapidly in recent years, which has abroad applications. There is little returns in home and few relevant papers published of core technology. In this paper, Visibility Culling, one of the key technologies of Virtual Reality Engine, has been studied, then an accelerate algorithms of Occlusion Culling has been provided.First, this paper introduces the technology of Virtual Reality synoptically, and expatiates the basic concept, identity, development, applications and investigation status of Virtual Reality at home and abroad, then introduces the architecture of Virtual Reality Engine as the core of the Virtual Reality System. The key technologies of Virtual Reality Engine are Collision detection, Visibility Culling, LOD and Illumination Model.Visibility Culling has three kinds: Backface Culling, Frustum Culling and Occlusion Culling.Frustum Culling is a simplified method which is from the other Frustum Culling, the result of the Frustum Culling is not ideal, but it run fast. However, Occlusion Culling is more complex, some needs large memory, others has long runtime, anther is suit for the fixed type of the object. Combining the extended projection proposed by Durand and hierachical occlusion map proposed by Greene et. al, the method can speed up the runtime and keep the conservative.To test the occlusion culling method, a simplified city model has been built with 3DS MAX 6.0, then exported to OpenGL for culling. Some parameters have been set up: scene-division:OBB; leaf size of bounding-volume-tree:10; Map resolution:256×256; view cell size:100; the number of occluders:100. The result is : the number of scene polygon is 3892, after Occlusion Culling, the number of the scene polygon get 2069, the ratio is 53%; after Occlusion Culling and Frustum Culling, the number of scene polygon is 769, the ratio is 20%.