Klaus H. Hinrichs

Managing uncertainty in moving objects databases

This article addresses the problem of managing Moving Objects Databases (MODs) which capture the inherent imprecision of the information about the moving objects location at a given time. We deal systematically with the issues of constructing and representing the trajectories of moving objects and querying the MOD. We propose to model an uncertain trajectory as a three-dimensional (3D) cylindrical body and we introduce a set of novel but natural spatio-temporal operators which capture the uncertainty and are used to express spatio-temporal range queries. We devise and analyze algorithms for processing the operators and demonstrate that the model incorporates the uncertainty in a manner which enables efficient querying, thus striking a balance between the modeling power and computational efficiency. We address some implementation aspects which we experienced in our DOMINO project, as a part of which the operators that we introduce have been implemented. We also report on some experimental observations of a practical relevance.

Efficient Bulk Operations on Dynamic R-trees

Abstract In recent years there has been an upsurge of interest in spatial databases. A major issue is how to manipulate efficiently massive amounts of spatial data stored on disk in multidimensional spatial indexes (data structures). Construction of spatial indexes (bulk loading ) has been studied intensively in the database community. The continuous arrival of massive amounts of new data makes it important to update existing indexes (bulk updating ) efficiently.In this paper we present a simple, yet efficient, technique for performing bulk update and query operations on multidimensional indexes. We present our technique in terms of the so-called R-tree and its variants, as they have emerged as practically efficient indexing methods for spatial data. Our method uses ideas from the buffer tree lazy buffering technique and fully utilizes the available internal memory and the page size of the operating system. We give a theoretical analysis of our technique, showing that it is efficient both in terms of I/ O communication, disk storage, and internal computation time. We also present the results of an extensive set of experiments showing that in practice our approach performs better than the previously best known bulk update methods with respect to update time, and that it produces a better quality index in terms of query performance. One important novel feature of our technique is that in most cases it allows us to perform a batch of updates and queries simultaneously. To be able to do so is essential in environments where queries have to be answered even while the index is being updated and reorganized.

Texturing techniques for terrain visualization

Presents a new rendering technique for processing multiple multi-resolution textures of LOD (level-of-detail) terrain models and describes its application to interactive, animated terrain content design. The approach is based on a multi-resolution model for terrain texture which cooperates with a multi-resolution model for terrain geometry. For each texture layer, an image pyramid and a texture tree are constructed. Multiple texture layers can be associated with one terrain model and can be combined in different ways, e.g. by blending and masking. The rendering algorithm simultaneously traverses the multi-resolution geometry model and the multi-resolution texture model, and takes into account geometric and texture approximation errors. It uses multi-pass rendering and exploits multi-texturing to achieve real-time performance. Applications include interactive texture lenses, texture animation and topographic textures. These techniques offer an enormous potential for developing new visualization applications for presenting, exploring and manipulating spatio-temporal data.

Arch-Explore: A natural user interface for immersive architectural walkthroughs

In this paper we propose the Arch-Explore user interface, which supports natural exploration of architectural 3D models at different scales in a real walking virtual reality (VR) environment such as head-mounted display (HMD) or CAVE setups. We discuss in detail how user movements can be transferred to the virtual world to enable walking through virtual indoor environments. To overcome the limited interaction space in small VR laboratory setups, we have implemented redirected walking techniques to support natural exploration of comparably large-scale virtual models. Furthermore, the concept of virtual portals provides a means to cover long distances intuitively within architectural models. We describe the software and hardware setup and discuss benefits of Arch-Explore.

Interactive Volume Rendering with Dynamic Ambient Occlusion and Color Bleeding

We propose a method for rendering volumetric data sets at interactive frame rates while supporting dynamic ambient occlusion as well as an approximation to color bleeding. In contrast to ambient occlusion approaches for polygonal data, techniques for volumetric data sets have to face additional challenges, since by changing rendering parameters, such as the transfer function or the thresholding, the structure of the data set and thus the light interactions may vary drastically. Therefore, during a preprocessing step which is independent of the rendering parameters we capture light interactions for all combinations of structures extractable from a volumetric data set. In order to compute the light interactions between the different structures, we combine this preprocessed information during rendering based on the rendering parameters defined interactively by the user. Thus our method supports interactive exploration of a volumetric data set but still gives the user control over the most important rendering parameters. For instance, if the user alters the transfer function to extract different structures from a volumetric data set the light interactions between the extracted structures are captured in the rendering while still allowing interactive frame rates. Compared to known local illumination models for volume rendering our method does not introduce any substantial rendering overhead and can be integrated easily into existing volume rendering applications. In this paper we will explain our approach, discuss the implications for interactive volume rendering and present the achieved results.

Implementation of the grid file: design concepts and experience

The grid file is an adaptable, symmetric multikey file structure. It stores highly dynamic sets of multidimensional data in such a way that different types of queries can be performed using few disk accesses. We present the design concepts underlying our implementation of the grid file and describe applications of thegrid file system.

Overlaying simply connected planar subdivisions in linear time

We present an algorithm which computes the overlay Hb r+ rIg of two Simply connected planar subdivisions ~b and Hg; we assume that ~b (resp. ~) and all its components are colored in blue (resp. green). The algorithm runs in O(n + k) time and space, where n denotes the total nuruber of edges of ~b and IIg and k the number of intersections between blue and green edges.

Uncertainty-Aware Guided Volume Segmentation

Although direct volume rendering is established as a powerful tool for the visualization of volumetric data, efficient and reliable feature detection is still an open topic. Usually, a tradeoff between fast but imprecise classification schemes and accurate but time-consuming segmentation techniques has to be made. Furthermore, the issue of uncertainty introduced with the feature detection process is completely neglected by the majority of existing approaches.In this paper we propose a guided probabilistic volume segmentation approach that focuses on the minimization of uncertainty. In an iterative process, our system continuously assesses uncertainty of a random walker-based segmentation in order to detect regions with high ambiguity, to which the users attention is directed to support the correction of potential misclassifications. This reduces the risk of critical segmentation errors and ensures that information about the segmentations reliability is conveyed to the user in a dependable way. In order to improve the efficiency of the segmentation process, our technique does not only take into account the volume data to be segmented, but also enables the user to incorporate classification information. An interactive workflow has been achieved by implementing the presented system on the GPU using the OpenCL API. Our results obtained for several medical data sets of different modalities, including brain MRI and abdominal CT, demonstrate the reliability and efficiency of our approach.

An object-oriented approach for integrating 3D visualization systems and GIS

Abstract Visualization has become an integral part in many applications of GIS. Due to the rapid development of computer graphics, visualization and animation techniques, general-purpose GIS can no longer satisfy the multitude of visualization demands. Therefore, GIS have to utilize independent visualization toolkits. This article examines how visualization systems can be used with and integrated into GIS. We analyze several key characteristics visualization toolkits should satisfy in order to be used efficiently by GIS. We show how GIS can provide visualization and animation features for geo objects by embedding the visualization system using object-oriented techniques. The concepts are described along with a new visualization and animation toolkit which provides extensible object-oriented technology for the development of visualization components for 2D, 3D and time-varying data. The design of this visualization toolkit concentrates on a seamless integration of application-specific geo-data into visualization components, an open interface for different rendering techniques and an advanced management of data dynamics.

Object‐oriented 3D Modelling, Animation and Interaction

We present an object-oriented 3D graphics and animation framework which provides a new methodology for the symmetric modelling of geometry and behaviour. The toolkit separates the specification of geometry and behaviour by two types of directed acyclic graphs, the geometry graph and the behaviour graph, which are linked together through constraint relations. All geometry objects and behaviour objects are represented as DAG nodes. The geometry graph provides a renderer-independent hierarchical description of 3D scenes and rendering processes. The behaviour graph specifies time- and event-dependent constraints applied to graphics objects. Behaviour graphs simplify the specification of complex animations and 3D interactions by providing nodes for the management of the time and event flow (e.g. durations, time layouts, time repeaters, actions). Nodes contain, manipulate and share instances of constrainable graphical abstract data types. Geometry nodes and behaviour nodes are used to configure high-level 3D widgets, i.e. high-level building blocks for constructing 3D applications. The fine-grained object structure of the system leads to an extensible reusable framework which can be implemented efficiently.