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

Shadow Techniques for Interactive and Real-Time Applications

Shadows provide important visual cues for the relative position of objects in threedimensional space. For interactive and real-time applications, e.g. in virtual reality systems or games, the shadow computation needs to be extremely fast, usually synchronized with the displays refresh rate. Using dynamic scenes with many, movable light sources, shadow computation is therefore often the main bottleneck in a rendering system. In this thesis we will discuss this problem in detail: Originating from Williams shadow maps and Crows shadow volumes, we will present hardware accelerated shadow techniques that are able to generate shadows of high-quality while still being fast enough to be used in real-time or interactive applications. We will show algorithms for the computation of hard shadows as well as for the more complex problem of approximating soft shadows caused by area light sources.Schatten sind wichtige visuelle Merkmale die über die relative Position eines Objektes in einem drei-dimensionalen Raum Aufschluss geben. Die Schattenberechnung muss für interaktive und Echtzeit-Anwendungen, wie z.B. Virtual Reality Systeme oder in Spielen, extrem schnell erfolgen, idealerweise synchronisiert mit der Bildwiederholfrequenz. Im Fall von dynamischen Szenen mit vielen, beweglichen Lichtquellen, ist die Berechnung von Schatten oftmals der zeitkritischste Teil innerhalb eines Rendering-Systems. In dieser Dissertation behandeln wir genau dieses Problem im Detail. Ausgehend vonWilliams\u27; Shadow Maps und Crow\u27;s Shadow Volumes werden Hardwarebeschleunigte Schattentechniken vorgestellt, die Schatten von hoher Qualität erzeugen können, aber trotzdem so effizient sind, dass sie für Echtzeit- und interaktive Anwendungen eingesetzt werden können. Wir werden sowohl Algorithmen zur Berechnung harter Schatten beschreiben, als auch das schwierigere Problem der Approximation von sanften Schatten, wie sie z.B. bei Flächenlichtquellen entstehen, behandeln

Fast and Accurate Visibility Preprocessing

Visibility culling is a means of accelerating the graphical rendering of geometric models. Invisible objects are efficiently culled to prevent their submission to the standard graphics pipeline. It is advantageous to preprocess scenes in order to determine invisible objects from all possible camera views. This information is typically saved to disk and may then be reused until the model geometry changes. Such preprocessing algorithms are therefore used for scenes that are primarily static. Currently, the standard approach to visibility preprocessing algorithms is to use a form of approximate solution, known as conservative culling. Such algorithms over-estimate the set of visible polygons. This compromise has been considered necessary in order to perform visibility preprocessing quickly. These algorithms attempt to satisfy the goals of both rapid preprocessing and rapid run-time rendering. We observe, however, that there is a need for algorithms with superior performance in preprocessing, as well as for algorithms that are more accurate. For most applications these features are not required simultaneously. In this thesis we present two novel visibility preprocessing algorithms, each of which is strongly biased toward one of these requirements. The first algorithm has the advantage of performance. It executes quickly by exploiting graphics hardware. The algorithm also has the features of output sensitivity (to what is visible), and a logarithmic dependency in the size of the camera space partition. These advantages come at the cost of image error. We present a heuristic guided adaptive sampling methodology that minimises this error. We further show how this algorithm may be parallelised and also present a natural extension of the algorithm to five dimensions for accelerating generalised ray shooting. The second algorithm has the advantage of accuracy. No over-estimation is performed, nor are any sacrifices made in terms of image quality. The cost is primarily that of time. Despite the relatively long computation, the algorithm is still tractable and on average scales slightly superlinearly with the input size. This algorithm also has the advantage of output sensitivity. This is the first known tractable exact solution to the general 3D from-region visibility problem. In order to solve the exact from-region visibility problem, we had to first solve a more general form of the standard stabbing problem. An efficient solution to this problem is presented independently