Conservative occlusion culling for urban visualization using a slice-wise data structure

Cataloged from PDF version of article.In this paper, we propose a framework for urban visualization using a conservative from-region visibility algorithm based on occluder shrinking. The visible geometry in a typical urban walkthrough mainly consists of partially visible buildings. Occlusion-culling algorithms, in which the granularity is buildings, process these partially visible buildings as if they are completely visible. To address the problem of partial visibility, we propose a data structure, called slice-wise data structure, that represents buildings in terms of slices parallel to the coordinate axes. We observe that the visible parts of the objects usually have simple shapes. This observation establishes the base for occlusion-culling where the occlusion granularity is individual slices. The proposed slice-wise data structure has minimal storage requirements. We also propose to shrink general 3D occluders in a scene to find volumetric occlusion. Empirical results show that significant increase in frame rates and decrease in the number of processed polygons can be achieved using the proposed slice-wise occlusion-culling as compared to an occlusion-culling method where the granularity is individual buildings. © 2007 Elsevier Inc. All rights reserved

Efficient Real-Time Rendering of Building Information Models

A Building Information Model (BIM) is a powerful concept, since it allows both 2D-drawings and 3D-models of buildings or facilities to be extracted from the same source of data. Compared to a general 3D-CAD model a BIM is a different kind of representation, since it defines not only geometrical data but also information regarding spatial relations and semantics. However, because of the large number of individual objects and high geometric complexity, 3D-data obtained from a BIM are not easily used for real-time rendering without further processing. In this paper we present a culling system specifically designed for efficient real-time rendering of BIM’s. By utilizing the unique properties of a BIM we can form the required data structures without manual modification or expensive preprocessing of the input data. Using hardware occlusion queries together with additional mechanisms based on specific BIM-data, the presented system achieves good culling efficiency for both indoor and outdoor cases

Conservative Visibility Preprocessing Using Extended Projections

International audienceVisualisation of very complex environments can be significantly accelerated using occlusion culling. In this paper we present a visibility preprocessing method which efficiently computes potentially visible geometry for volumetric viewing cells. We introduce novel extended projection operators, which permits efficient occlusion culling with respect to all viewpoints within a cell, and takes into account the combined occlusion effect of multiple occluders. We use extended projection of occluders onto a set of projection planes to create extended occlusion maps; we show how to efficiently test occludees against these occlusion maps to determine occlusion with respect to the entire cell. We also present an improved projection operator for certain specific but important configurations. An important advantage of our approach is that we can re-project extended projections onto a series of projection planes (via an occlusion sweep), and thus accumulate occlusion information from multiple blockers. This new approach allows the creation of effective occlusion maps for previously hard-to-treat scenes such as leaves of trees in a forest. Graphics hardware is used to accelerate both the extended projection and reprojection operations. We present a complete implementation of our preprocessing algorithm demonstrating significant speedup with respect to view-frustum culling only, without the computational overhead of on-line occlusion culling

Time and Space Coherent Occlusion Culling for Tileable Extended 3D Worlds

International audienceIn order to interactively render large virtual worlds, the amount of 3D geometry passed to the graphics hardware must be kept to a minimum. Typical solutions to this problem include the use of potentially visible sets and occlusion culling, however, these solutions do not scale well, in time nor in memory, with the size of a virtual world. We propose a fast and inexpensive variant of occlusion culling tailored to a simple tiling scheme that improves scalability while maintaining very high performance. Tile visibilities are evaluated with hardwareaccelerated occlusion queries, and in-tile rendering is rapidly computed using BVH instantiation and any visibility method; we use the CHC++ occlusion culling method for its good general performance. Tiles are instantiated only when tested locally for visibility, thus avoiding the need for a preconstructed global structure for the complete world. Our approach can render large-scale, diversified virtual worlds with complex geometry, such as cities or forests, all at high performance and with a modest memory footprint

Erosion Based Visibility Preprocessing

International audienceThis paper presents a novel method for computing visibility in 2.5D environments. It is based on a novel theoretical result: the visibility from a region can be conservatively estimated by computing the visibility from a point using appropriately "shrunk" occluders and occludees. We show how approximated but yet conservative shrunk objects can efficiently be computed in a urban environment. The application of this theorem provides a tighter potentially visible set (PVS) than the original method it is built on. Finally, theoretical implications of the theorem are discussed, and we believe it can open new research directions

Visualization of urban environments

Ankara : The Department of Computer Engineering and the Institute of Engineering and Science of Bilkent University, 2007.Thesis (Ph. D.) -- Bilkent University, 2007.Includes bibliographical references leaves 108-118Modeling and visualization of large geometric environments is a popular research area in computer graphics. In this dissertation, a framework for modeling and stereoscopic visualization of large and complex urban environments is presented. The occlusion culling and view-frustum culling is performed to eliminate most of the geometry that do not contribute to the user’s final view. For the occlusion culling process, the shrinking method is employed but performed using a novel Minkowski-difference-based approach. In order to represent partial visibility, a novel building representation method, called the slice-wise representation is developed. This method is able to represent the preprocessed partial visibility with huge reductions in the storage requirement. The resultant visibility list is rendered using a graphics-processing-unit-based algorithm, which perfectly fits into the proposed slice-wise representation. The stereoscopic visualization depends on the calculated eye positions during walkthrough and the visibility lists for both eyes are determined using the preprocessed occlusion information. The view-frustum culling operation is performed once instead of two for both eyes. The proposed algorithms were implemented on personal computers. Performance experiments show that, the proposed occlusion culling method and the usage of the slice-wise representation increase the frame rate performance by 81 %; the graphics-processing-unit-based display algorithm increases it by an additional 315 % and decrease the storage requirement by 97 % as compared to occlusion culling using building-level granularity and not using the graphics hardware. We show that, a smooth and real-time visualization of large and complex urban environments can be achieved by using the proposed framework.Yılmaz, TürkerPh.D

Stereoscopic urban visualization based on graphics processor unit

We propose a framework for the stereoscopic visualization of urban environments. The framework uses occlusion and view-frustum culling (VFC) and utilizes graphics hardware to speed up the rendering process. The occlusion culling is based on a slice-wise storage scheme that represents buildings using axis-aligned slices. This provides a fast and a low-cost way to access the visible parts of the buildings. View-frustum culling for stereoscopic visualization is carried out once for both eyes by applying a transformation to the culling location. Rendering using graphics hardware is based on the slice-wise building representation. The representation facilitates fast access to data that are pushed into the graphics procesing unit (GPU) buffers. We present algorithms to access this GPU data. The stereoscopic visualization uses off-axis projection, which we found more suitable for the case of urban visualization. The framework is tested on large urban models containing 7.8 million and 23 million polygons. Performance experiments show that real-time stereoscopic visualization can be achieved for large models. © 2008 Society of Photo-Optical Instrumentation Engineers

Implementing software occlusion culling for real-time applications

The visualization of complex virtual scenes can be significantly accelerated by applying Occlusion Culling. In this work we introduce a variant of the Hierarchical Occlusion Map method to be used in Real-Time applications. To avoid using real objects geometry we generate specialized conservative Occluders based on Axis Aligned Bounding Boxes which are converted into coplanar quads and then rasterized in CPU using a downscaled Depth Buffer. We implement this method in a 3D scene using a software occlusion map rasterizer module specifically optimized to rasterize Occluder quads into a Depth Buffer. We demonstrate that this approach effectively increases the number of occluded objects without generating significant runtime overhead.Eje: Workshop Computación gráfica, imágenes y visualización (WCGIV)Red de Universidades con Carreras en Informática (RedUNCI

Accelerating Virtual Walkthrough with Visual Culling Techniques

Abstract-Virtual walkthrough application allows users to navigate and immerse in the generated 3D environment with computer graphics assist. The 3D environment requires a large amount of geometry to make it look realistic. When the number of geometry increase, the performance of the application will become slower. Consequently, it creates a conflict between the needs of realistic and real time. In this paper, we discuss the implementation of visual culling techniques such as view frustum culling, back face culling and occlusion culling in the virtual walkthrough application. We render only what we can see during the application runtime and cull away unnecessary geometry. This will accelerate the performance of the system. Without the culling techniques implemented in virtual reality application such as virtual walkthrough, the system has to allocate a large space of memory to store the geometry data. We have tested these techniques to the Ancient Malacca data. With the visual culling techniques implemented, the virtual walkthrough system can work in real time mode without scarifying realism factor