A Toolset for Visualization, Interaction, and Rendering in Virtual Environments

Diese Arbeit beschäftigt sich mit einigen der interessantesten Kernpunkten der Erstellung eines VR-Systems: die Vorbereitung und Vorverarbeitung der Daten, deren Visualisierung, die Interaktion mit den Daten und deren Darstellung. Es werden problem-zugeschnittene Algorithmen, sowie allgemeine Strategien zur Lösung der entstehenden Probleme vorgestellt. Insbesondere wird ein neuer Algorithmus zur Segmentierung von Bild- und Volumendaten eingeführt, der vor allem für medizinische Anwendungen relevant ist. Weiterhin wird detailliert die Visualisierung von Daten erläutert, die einen Zeitparameter enthalten. Dabei wird eine Reihe von Visualisierungs- und Interaktionswerkzeugen zur Analyse historischer Daten demonstriert. Desweiteren wird der Frage nach der Navigation und der Manipulation entfernter Objekte nachgegangen und eine neue Interaktionsmetapher vorgestellt: die Durch-Die-Linse-Metapher (through-the-lens). Basierend auf diesem Konzept werden verschiedene Navigationswerkzeuge präsentiert, die die Eigenschaften bekannter Techniken instrumentalisieren, jedoch deren Einschränkungen umgehen und eine leistungsfähige Interaktion ermöglichen. Schließlich werden zwei Algorithmen vorgestellt, die eine schnelle Darstellung der zu visualisierenden Daten in einer virtuellen Umgebung ermöglichen. Jeder dieser Algorithmen nutzt typische Eigenschaften der Repräsentation. Erstens wird ein bild-basierter Ansatz vorgestellt, der auf Merkmalen des Durch-Die-Linse-Konzeptes beruht. Zweitens wird auf die Stereo-Ausgabe von großen Szenen im Allgemeinen eingegangen.This work addresses some of the most pressing issues considering the assembly of a virtual reality system: the data preprocessing and preparation, the data visualization, the interaction with the data, and their display. The work presents problem-tailored algorithms, as well as general strategies for tackling the introduced problems. In particular, a new algorithm for segmenting image and volume data is discussed, addressing foremost medical applications in general. Moreover, a detailed discussion on visualization issues of data containing a time dimension is provided, demonstrating a set of visualization and interaction props for the analysis of historical events in time. We describe a set of tools for simultaneously visualization of various parameters of interest and for interactive study of historical events. In addition, the navigation in general is analyzed, as well as the remote object manipulation in virtual environments, presenting a new interaction metaphor: the through-the-lens metaphor. Based on this new concept, a set of navigation tools is introduced, which exploit features of existing techniques, attempting to overcome their limitations and to enable more powerful interaction. Finally, in order to enable fast rendering of the visualized data, two algorithms for accelerating the rendering performance of a virtual reality system are proposed. Each of them exploits particular characteristics of the representation: (1) an image-based rendering approach based on the features of the introduced through-the-lens tools is presented, (2) the stereo rendering of large scenes is addressed in general

RaFSi – a FastWatershed algorithm based on rainfalling simulation

In this paper, we present a fast watershed algorithm based on the rainfalling simulation. We present the various techniques and data structures utilized in our approach. Throughout this work, the processing of large data sets (images as well as volume data) is especially emphasized. The results’ correctness, the fast execution time, and the memory requirements are discussed in detail. First we introduce a sequential algorithm and discuss the cases, where the known algorithm produces erroneous results. Afterwards, the presented watershed algorithm is compared with immersion based watershed algorithms with respect to running time and memory requirements

QteVtk - a Multi-Platform, Object-Oriented Visualization Environment Extending VTK

In this study, we present a new comprehensive visualization environment, based on the VTK-library. We first introduce a window system independent graphical interface for the VTK-classes and it's object-oriented design, then we describe a set of viewer and editor classes for displaying and editing different data types available in the VTK-library. The described library (QteVtk) provides a graphical user interface (GUI) to ease creating VTK-visualization pipelines with graphical appearance. Furthermore, it implements saving, loading, and adjusting of objects and object parameters, while supporting VTK-concepts like object oriented design and ``demand driven'' update of the visualization pipeline for data-flow control. QteVtk provides for the first time an easy to use combination of a free object oriented visualization with multi-platform GUI elements. The presented work came into being, because in the authors' opinion the visualization still lacks a free, well designed, in terms of object oriented data structures and algorithms, but powerful and easy to use visualization library for implementing visualization applications with the latter, as well as adding new data structures and techniques to it

The Multi-LDI: an image based rendering approach for interaction navigation, and visualization in complex virtual environments

In this paper, we present a new data structure for image-based rendering: the multi LDI. The multi LDI consists of a number of Layered Depth Images (LDI) covering a hemisphere of possible viewing angles. It allows compact image-based storage and fast rendering of large and complex scenes, while supporting rendering from large range of viewing directions. Since the internal occlusion in each LDI is very small, and only one of the LDIs in the multi LDI is rendered at a time, the rendering cost is significantly reduced compared to geometry-based rendering and even compared to other image-based rendering methods. Moreover, the single LDIs in the multi LDI can be generated on demand using a number of depth images rendered with an offscreen renderer. We also discuss a comparison of the geometry-based rendering and our image-based method and present some measured rendering times. Furthermore, we describe the utilization of this technique in a complex Virtual Environment (VE) for realizing navigation, visualization, and interaction aids. In particular, we present a multiple viewport technique providing two important features: (1) A sort of history during the modeling process, whereas a live 3D copy of the scene is displayed in a window in front of the user. (2) Different live views of the scene, seen from arbitrary viewpoints, in order to display details occluded in the normal view

Accelerated Rendering in Stereo-Based Projections

In this work, we present a new method for displaying stereo scenes, which speeds up the rendering time of complex geometry. We first discuss a scene splitting strategy, allowing us to partition objects to the distant background or the near foreground. Furthermore, wededuce a computation rule for positioning a cutting plane in the scene. 1