Real-time rendering of triangulated surfaces has attracted growing interest in the last few years. However, interactive visualization of very large scale grid digital elevation models is still a hard problem. The graphics load must be controlled by an adaptive surface triangulation and by taking advantage of different levels of detail. Furthermore, the management of the visible scene requires efficient access to the terrain database. We describe a all-in-one visualization system which integrates adaptive triangulation, dynamic scene management and spatial data handling. The triangulation model is based on the restricted quadtree triangulation. Furthermore, we present new algorithms of the restricted quadtree triangulation. These include among others exact error approximation, progressive meshing, performance enhancements and spatial access. Keywords algorithms, computer graphics, virtual reality, triangulated surfaces, terrain visualization, terascale visualization 1. Introduction In...

Real-time rendering and multiresolution modeling of triangulated surfaces has attracted growing interest over the last decade. For interactive visualization of very large scale grid digital elevation models efficiency is a particularly important aspect. The graphics rendering load must be controlled by reducing the number of rendered primitives using level-of-detail (LOD) techniques, adaptive extraction of LOD triangle meshes in main memory must be performed at interactive frame rates, and loading-on-demand of elevation data from secondary storage has to be highly efficient as well. Due to the high regularity of grid digital elevation models, hierarchical quadtree based terrain triangulation models have been shown to be among the most efficient methods available. In this paper we will survey and compare several approaches that follow this quadtree based surface decomposition and triangulation.

The maintenance of large raster images under spatial operations is still a major performance bottleneck. For reasons of storage space, images in a collection, such as satellite pictures in geographic information systems, are maintained in compressed form. Instead of performing a spatially selective operation on an image by first decompressing the compressed version, we propose in this paper to perform queries directly on the compressed version of the image. We suggest a compression technique that allows for the subsequent use of a spatial index structure to guide a spatial search. In response to a window query, our algorithm delivers a compressed partial image, or the exact uncompressed requested image region. In addition to the support of spatial queries on compressed continuous tone images, the new compression algorithm is even competitive in terms of the compression ratio that it achieves, compared to other standard lossless compression techniques. Index Terms---Lossless image comp...

This paper presents aspects of the implementation of a bidirectional link between the Geographic Information System (GIS) ArcView 3.0 and the interactive dynamic statistical graphics program XGobi. We describe the main functionality of the link, the underlying Remote Procedure Call (RPC) mechanism, and internal data structures, and discuss topics such as security, concurrency, and linked brushing. We think that these topics are of particular interest to software authors intending to link similar software packages, and software users learning about strengths (and weaknesses) of the implementation of our link.

This thesis describes a web-based, responsive, zooming and panning visualization system for a full-featured geographic description of the United States. Current web-based map servers provide, from a visualization standpoint, little more than one static image per page, with hyperlinks for navigation; continuous zooming and panning requires locally stored data. Our primary contribution is a multi-threaded, scalable and responsive client-server architecture that responds to user requests as naturally and quickly as possible, regardless of network bandwidth reliability. This architecture can be generalized for use in other applications, including non-geographic ones. To this we add a scalable and exible user interface for navigation of multi-scale geographic data, with intuitive zooming and panning, pop-up feature labels, and a user controlled tree-hierarchy of windows. We build software tools and algorithms for translating the U.S. Census Bureau's TIGER data into a format designed for speedy database retrieval and network delivery, and for generalizing the data into multiple levels of detail. Because of anomalies in the TIGER data, this processing requires some human intervention. v vi Contents Acknowledgments iii Abstract v List of Figures xi List of Tables xiii 1

In this paper we report on a linked environment of the three programs XGobi, XploRe, and ViRGIS. While XGobi and XploRe are statistical packages that focus on dynamic statistical graphics and provide analytical statistical features, respectively, ViRGIS is a 3D Virtual Reality Geographic Information System (GIS) that allows real--time access to, and visualization of, geographic data. The XGobi/XploRe/ViRGIS environment is based on the Remote Procedure Call (RPC) technology previously developed for the ArcView/XGobi/XploRe environment. It allows linked brushing and the exchange of data and commands --- completely transparent to the user. 1. Introduction In our previous work, we developed an open software system consisting of the Geographic Information System (GIS) ArcView, the dynamic statistical graphics program XGobi, and the statistical computing environment XploRe (Symanzik, Kotter, Schmelzer, Klinke, Cook & Swayne 1998, Symanzik, Cook, Klinke & Lewin 1998). In this current projec...

This paper describes a decade's worth of evolution of integrating software to support exploratory spatial data analysis (ESDA) where there are multiple measured attributes. The multivariate graphics tools we use are XGobi, and more recently, GGobi. The paper is divided into two parts. In the first part, we review early experiments in software linking for ESDA, which used XGobi, di#erent Geographic Information Systems (GIS), and the statistical analysis packages S and XploRe. We discuss applications, capabilities and deficits of these existing links. In the second part we describe GGobi, the descendant of XGobi, which was designed with software integration as a fundamental goal. GGobi lends itself to broader possibilities for linking with other software for richer ESDA.

This thesis describes a web-based, responsive, zooming and panning visualization system for a full-featured geographic description of the United States. Current web-based map servers provide, from a visualization standpoint, little more than one static image per page, with hyperlinks for navigation; continuous zooming and panning requires locally stored data. Our primary contribution is a multi-threaded, scalable and responsive client-server architecture that responds to user requests as naturally and quickly as possible, regardless of network bandwidth reliability. This architecture can be generalized for use in other applications, including non-geographic ones. To this we add a scalable and flexible user interface for navigation of multi-scale geographic data, with intuitive zooming and panning, pop-up feature labels, and a user controlled tree-hierarchy of windows. We build software tools and algorithms for translating the U.S. Census Bureau’s TIGER data into a format designed for speedy database retrieval and network delivery, and for generalizing the data into multiple levels of detail. Because of anomalies in the TIGER data, this processing requires some human intervention.