Research On Portal Generation Methods In Fast Rendering Of Large Scenes

In virtual reality systems, the rendering engines need render a high-quality complex scene quickly to provide real-time interaction, which require the development in the techniques of accelerating the rendering of large scenes. Some visibility culling algorithms like the one based on cell and portal can be used to accelerate it. The portal technique aims at partitioning the scene into cells and portals, based on which visibility culling can be applied. It has been widely used in virtual environment. However, a big problem arises as to how to position the portals automatically for a large scene. There exist many methods for it, but many are with the disadvantage of over-segmentation. That's, the scene is divided into excessive invalid cells and portals.The technique of region merging is brought up for solving the problem of over-segmentation in 2- or 3- dimension environments. Based on the characteristics of a valid partitioning, it evaluates the partitioning result and merges the cells evaluated as invalid. As to a 3-dimension indoor scene, the technique of region merging plays an important role in keeping a reasonable partitioning, eliminating the excessive invalid portals, and consequently reducing the PVS and accelerating the rendering of large scenes.In this paper the problems and requirements of rendering large scenes are presented first. Then some accelerating methods like the one based on portal and cell are introduced. In chapter 2 some portal generation methods for 3-d scenes are explained. After presenting the problem of over-segmentation which is facing many portal-generation methods, the technique of region merging is brought forward as a solution. Some methods for region merging of 2-dimension images are introduced with their advantages and disadvantages discussed. In chapter 3 a portal-generation method, to which our improved region merging technique is to be applied, is introduced in detail. Its problem of over-segmentation and requirement for region merging technique is also presented. In chapter 4, some related subjects for merging 3-dimension regions are discussed and the proposed solution is illustrated, with aprinciple for testing the dissimilarity of 2 regions proposed. Then, how to apply the improved technique into the portal-generation method is explained in detail. The main contributions of this paper are a new region-merging method for 3-d environment and its application in portal generation method. Compared to the original portal generation method, after applying the improved region merging technique, it provides a better partitioning result. In chapter 5, some drawbacks and future work are presented.