Knowledge-based out-of-core algorithms for data management in visualization

Journal ArticleData management is the very first issue in handling very large datasets. Many existing out-of-core algorithms used in visualization are closely coupled with application-specific logic. This paper presents two knowledgebased out-of-core prefetching algorithms that do not use hard-coded rendering-related logic. They acquire the knowledge of the access history and patterns dynamically, and adapt their prefetching strategies accordingly. We have compared the algorithms with a demand-based algorithm, as well as a more domain-specific out-of-core algorithm. We carried out our evaluation in conjunction with an example application where rendering multiple point sets in a volume scene graph put a great strain on the rendering algorithm in terms of memory management. Our results have shown that the knowledge-based approach offers a better cache-hit to disk-access trade-off. This work demonstrates that it is possible to build an out-of-core prefetching algorithm without depending on rendering-related application-specific logic. The knowledge based approach has the advantage of being generic, efficient, flexible and self-adaptive

Combining Point Clouds and Volume Objects in Volume Scene Graphs

This paper describes an extension to the technical framework of Constructive Volume Geometry (CVG) in order to accommodate point clouds in volume scene graphs. It introduces the notion of point-based volume object (PBVO) that is characterized by the opacity, rather than the geometry, of a point cloud. It examines and compares several radial basis functions (RBFs), including the one proposed in this paper, for constructing scalar fields from point clouds. It applies basic CVG operators to PBVOs and demonstrates the inter-operability of PBVOs with conventional volume objects including those procedurally defined and those constructed from volume datasets. It presents an octree-based algorithm for reducing the complexity in rendering a PBVO with a large number of points, and a set of testing results showing a significant speedup when an octree is deployed for rendering PBVOs

High-dimensional glyph-based visualization and interactive techniques.

The advancement of modern technology and scientific measurements has led to datasets growing in both size and complexity, exposing the need for more efficient and effective ways of visualizing and analysing data. Despite the amount of progress in visualization methods, high-dimensional data still poses a number of significant challenges in terms of the technical ability of realising such a mapping, and how accurate they are actually interpreted. The different data sources and characteristics which arise from a wide range of scientific domains as well as specific design requirements constantly create new special challenges for visualization research. This thesis presents several contributions to the field of glyph-based visualization. Glyphs are parametrised objects which encode one or more data values to its appearance (also referred to as visual channels) such as their size, colour, shape, and position. They have been widely used to convey information visually, and are especially well suited for displaying complex, multi-faceted datasets. Its major strength is the ability to depict patterns of data in the context of a spatial relationship, where multi-dimensional trends can often be perceived more easily. Our research is set in the broad scope of multi-dimensional visualization, addressing several aspects of glyph-based techniques, including visual design, perception, placement, interaction, and applications. In particular, this thesis presents a comprehensive study on one interaction technique, namely sorting, for supporting various analytical tasks. We have outlined the concepts of glyph- based sorting, identified a set of design criteria for sorting interactions, designed and prototyped a user interface for sorting multivariate glyphs, developed a visual analytics technique to support sorting, conducted an empirical study on perceptual orderability of visual channels used in glyph design, and applied glyph-based sorting to event visualization in sports applications. The content of this thesis is organised into two parts. Part I provides an overview of the basic concepts of glyph-based visualization, before describing the state-of-the-art in this field. We then present a collection of novel glyph-based approaches to address challenges created from real-world applications. These are detailed in Part II. Our first approach involves designing glyphs to depict the composition of multiple error-sensitivity fields. This work addresses the problem of single camera positioning, using both 2D and 3D methods to support camera configuration based on various constraints in the context of a real-world environment. Our second approach present glyphs to visualize actions and events "at a glance". We discuss the relative merits of using metaphoric glyphs in comparison to other types of glyph designs to the particular problem of real-time sports analysis. As a result of this research, we delivered a visualization software, MatchPad, on a tablet computer. It successfully helped coaching staff and team analysts to examine actions and events in detail whilst maintaining a clear overview of the match, and assisted in their decision making during the matches. Abstract shortened by ProQuest

Hardware accelerated volume texturing.

The emergence of volume graphics, a sub field in computer graphics, has been evident for the last 15 years. Growing from scientific visualization problems, volume graphics has established itself as an important field in general computer graphics. However, the general graphics fraternity still favour the established surface graphics techniques. This is due to well founded and established techniques and a complete pipeline through software onto display hardware. This enables real-time applications to be constructed with ease and used by a wide range of end users due to the readily available graphics hardware adopted by many computer manufacturers. Volume graphics has traditionally been restricted to high-end systems due to the complexity involved with rendering volume datasets. Either specialised graphics hardware or powerful computers were required to generate images, many of these not in real-time. Although there have been specialised hardware solutions to the volume rendering problem, the adoption of the volume dataset as a primitive relies on end-users with commodity hardware being able to display images at interactive rates. The recent emergence of programmable consumer level graphics hardware is now allowing these platforms to compute volume rendering at interactive rates. Most of the work in this field is directed towards scientific visualisation. The work in this thesis addresses the issues in providing real-time volume graphics techniques to the general graphics community using commodity graphics hardware. Real-time texturing of volumetric data is explored as an important set of techniques in delivering volume datasets as a general graphics primitive. The main contributions of this work are; The introduction of efficient acceleration techniques; Interactive display of amorphous phenomena modelled outside an object defined in a volume dataset; Interactive procedural texture synthesis for volume data; 2D texturing techniques and extensions for volume data in real-time; A flexible surface detail mapping algorithm that removes many previous restrictions Parts of this work have been presented at the 4th International Workshop on Volume Graphics and also published in Volume Graphics 2005

Autonomic visualisation.

This thesis introduces the concept of autonomic visualisation, where principles of autonomic systems are brought to the field of visualisation infrastructure. Problems in visualisation have a specific set of requirements which are not always met by existing systems. The first half of this thesis explores a specific problem for large scale visualisation; that of data management. Visualisation algorithms have somewhat different requirements to other external memory problems, due to the fact that they often require access to all, or a large subset, of the data in a way that is highly dependent on the view. This thesis proposes a knowledge-based approach to pre-fetching in this context, and presents evidence that such an approach yields good performance. The knowledge based approach is incorporated into a five-layer model, which provides a systematic way of categorising and designing out-of-core, or external memory, systems. This model is demonstrated with two example implementations, on in the local and one in the remote context. The second half explores autonomic visualisation in the more general case. A simulation tool, created for the purpose of designing autonomic visualisation infrastructure is presented. This tool, SimEAC, provides a way of facilitating the development of techniques for managing large-scale visualisation systems. The abstract design of the simulation system, as well as details of the implementation are presented. The architecture of the simulator is explored, and then the system is evaluated in a number of case studies indicating some of the ways in which it can be used. The simulator provides a framework for experimentation and rapid prototyping of large scale autonomic systems