Culling for time critical rendering of complex virtual environments

Abstract

Systems for interactive visualization or virtual reality (VR) should maintain a suitable update rate for display according to users```` input. To satisfy this requirement of display performance, the rendering process of visualization systems should be executed within a fixed time, so it is a time critical process. In this thesis, we discuss an approach of scene culling that culls potentially invisible polygons from scene polygons composing a complex virtual environment, and then rendering the scene rapidly with only potentially visible polygons. The culling process mainly consists of two parts. The first part subdivides the viewpoint space into subspaces or cells, and precalculates potentially visible polygons for each cell before interactive visualization. The second part as one of processes for interactive visualization finds the cell where the viewpoint currently resides and fetches the potentially visible polygons that were precalculated for the cell. If the number of fetched polygons is too large to achieve the target display performance, then an additional culling is performed in realtime for the current viewpoint. We propose a conservative visibility preprocessing method that is applicable to virtual environments modeled on outdoor scenes like city. The "conservative" word means finding potentially visible polygons or a superset of visible polygons from a three-dimensional space other than the exact set of visible polygons. The proposed method deals with invisible polygons jointly blocked by multiple occluders to compute a tight superset and enhance the culling result. In the proposed method, we express the four-dimensional information of area visibility onto two-dimensional spaces and keep it with a TSP (ternary space partitioning) tree. We perform the visibility test by constructing and traversing a TSP tree. In the proposed method, users can make a suitable tradeoff between the preprocessing time or memory usage and the culling result by restricting ...