Google Earth as a virtual globe tool for Earth science applications at the global scale: progress and perspectives

Research on global environmental change requires new data processing and analysis tools that can integrate heterogeneous geospatial data from real-time in situ measurement, remote sensing (RS) and geographic information systems (GISs) at the global scale. The rapid growth of virtual globes for global geospatial information management and display holds promise to meet such a requirement. Virtual globes, Google Earth in particular, enable scientists around the world to communicate their data and research findings in an intuitive three-dimensional (3D) global perspective. Different from traditional GIS, virtual globes are low cost and easy to use in data collection, exploration and visualization. Since 2005, a considerable number of papers have been published in peer-reviewed journals and proceedings from a variety of disciplines. In this review, we examine the development and applications of Google Earth and highlight its merits and limitations for Earth science studies at the global scale. Most limitations are not unique to Google Earth, but to all virtual globe products. Several recent efforts to increase the functionalities in virtual globes for studies at the global scale are introduced. The power of virtual globes in their current generations is mostly restricted to functions as a ‘geobrowser’; a better virtual globe tool for Earth science and global environmental change studies is described.     

Visualizing and analyzing dynamic meteorological data with virtual globes: A case study of tropical cyclones

Visualization is an important component of the evaluation of meteorological models, forecasting research, and other applications. With advances in computing power, the volume of meteorological data generated by geoscience and climate researchers has been steadily increasing. The emerging technique of virtual globes has been regarded as an ideal platform for visualizing larger geospatial data over the Internet. To visualize and analyze meteorological data with the new virtual globes, this paper proposes a systematic meteorological data visualization (MDV) framework in World Wind, an open-source virtual globe. The key technologies, including a hierarchical octree-based multiresolution data organization, data scheduling, level of detail (LOD) and rendering are described in detail. The framework is then applied to a practical tropical cyclone simulation, including flow vectors, particle tracking, cross-sectional analysis, streamlines, pathway animation, and volume rendering. The results show that virtual globes are effective tools for meteorological data visualization and analysis.     

Capturing the dance of the earth: PolarGlobe: Real-time scientific visualization of vector field data to support climate science

This paper introduces a streamline visualization technique that empowers PolarGlobe, an interactive, virtual globe-based, multi-dimensional scientific visualization tool to facilitate the observation and visual inspection of changes in the climate in real time. Specifically, this technique achieves effective visualization of vector-based earth science data through an automated data processing pipeline which integrates novel strategies including random seeding, finer-granularity parallelization and real-time rendering. The random seeding strategy allows for a vivid visual effect and an interactive framerate regardless of the spatial resolution in the raw dataset. The visualization algorithm is designed to be naturally parallelizable by partitioning the rendering tasks of unsteady vector field into multiple subtasks such that high-performance rendering can be realized. The platform is capable of taking either irregular or regular gridded data as input, and through the proposed data (re)projection pipeline, an automatic transformation of spatially enabled scientific data from the original data projection to the 3D globe-based virtual space is achieved. A series of experiments was conducted to identify the best configuration of rendering parameters to achieve the optimal rendering performance and visual effect. The results demonstrated the scalability and capability of the proposed PolarGlobe system to visualize big and unsteady vector flow data across different spatial and temporal scales. PolarGlobe implements former Vice President Al Gore's vision of a digital earth that enables scientists and citizens across the world to interactively study our planet. We expect the methods and techniques presented in this work to contribute significantly to both the scientific visualization and climate science communities.     

Region-of-interest visualization by CAVE VR system with automatic control of level-of-detail

To specify the region of interest (ROI) is an effective approach to visualize large scale simulation data. We have developed a three-dimensional visualization software with ROI function for the CAVE virtual reality systems. This software enables the user to perform fully three-dimensional and interactive visualization of large scale computational fluid dynamics (CFD) data. The user specifies a ROI in the CAVE room by a three-dimensional “mouse-drag”. The data in the specified ROI is automatically extracted from the original CFD data. This ROI procedure can be repeated recursively. The resolution in each ROI is kept approximately constant. A data set of three vector fields and eight scalar fields whose size is about 1 GB each was successfully analyzed.     

Visualizing dynamic geosciences phenomena using an octree-based view-dependent LOD strategy within virtual globes

Geoscientists build dynamic models to simulate various natural phenomena for a better understanding of our planet. Interactive visualizations of these geoscience models and their outputs through virtual globes on the Internet can help the public understand the dynamic phenomena related to the Earth more intuitively. However, challenges arise when the volume of four-dimensional data (4D), 3D in space plus time, is huge for rendering. Datasets loaded from geographically distributed data servers require synchronization between ingesting and rendering data. Also the visualization capability of display clients varies significantly in such an online visualization environment; some may not have high-end graphic cards. To enhance the efficiency of visualizing dynamic volumetric data in virtual globes, this paper proposes a systematic framework, in which an octree-based multiresolution data structure is implemented to organize time series 3D geospatial data to be used in virtual globe environments. This framework includes a view-dependent continuous level of detail (LOD) strategy formulated as a synchronized part of the virtual globe rendering process. Through the octree-based data retrieval process, the LOD strategy enables the rendering of the 4D simulation at a consistent and acceptable frame rate. To demonstrate the capabilities of this framework, data of a simulated dust storm event are rendered in World Wind, an open source virtual globe. The rendering performances with and without the octree-based LOD strategy are compared. The experimental results show that using the proposed data structure and processing strategy significantly enhances the visualization performance when rendering dynamic geospatial phenomena in virtual globes.     

Using NASA's World Wind virtual globe for interactive internet visualization of the global MODIS burned area product

Three‐dimensional virtual globes are radically changing the way geographic information is perceived by the public. This article describes how NASA World Wind, an open source virtual globe, is currently being used for visualization of the MODIS burned area product. The procedures adopted for converting the product into a format compatible with World Wind, as well as the spatial generalization of these data at different scales, are described. Directions to instructions on how to obtain the MODIS burned area product visualization imagery and use it in World Wind are included. This article highlights the potential benefits of integrating the visualization capability of virtual globes into the next generation of remotely sensed product internet analysis and distribution systems.     

Maps and Globes in Virtual Reality

This paper explores different ways to render world‐wide geographic maps in virtual reality (VR). We compare: (a) a 3D exocentric globe, where the user's viewpoint is outside the globe; (b) a flat map (rendered to a plane in VR); (c) an egocentric 3D globe, with the viewpoint inside the globe; and (d) a curved map, created by projecting the map onto a section of a sphere which curves around the user. In all four visualisations the geographic centre can be smoothly adjusted with a standard handheld VR controller and the user, through a head‐tracked headset, can physically move around the visualisation. For distance comparison exocentric globe is more accurate than egocentric globe and flat map. For area comparison more time is required with exocentric and egocentric globes than with flat and curved maps. For direction estimation, the exocentric globe is more accurate and faster than the other visual presentations. Our study participants had a weak preference for the exocentric globe. Generally the curved map had benefits over the flat map. In almost all cases the egocentric globe was found to be the least effective visualisation. Overall, our results provide support for the use of exocentric globes for geographic visualisation in mixed‐reality.     

Situation awareness and virtual globes: Applications for disaster management

This paper presents research on the use of virtual globes to support the development of disaster event situation awareness in humans via open source information analysis and visualization. The key technology used for this research is the Context Discovery Application (CDA), which is a geovisual analytic environment designed to integrate implicit geographic information with Google Earth™. A case study of humanitarian disaster management is used to demonstrate the unique abilities of the CDA and Google Earth^TM to support situation awareness. The paper provides some of the first empirical evidence on the utility of the virtual globes to support situation awareness for disaster management using implicit geographic information. The evidence presented was derived from evaluations by disaster management practitioners at the United Nations (UN) ReliefWeb project, an extremely relevant, yet difficult group to access for conducting academic disaster management research. Finally, ideas for future research on developing virtual globe applications to support situation awareness are described.     

A tropical cyclone application for virtual globes

Within the past ten years, a wide variety of publicly available environmental satellite-based data have become available to users and gained popular exposure in meteorological applications. For example, the Naval Research Laboratory (NRL) has maintained a well accepted web-based tropical cyclone (TC) website (NRL TC-Web) with a diverse selection of environmental satellite imagery and products covering worldwide tropical cyclones extending back to 1997. The rapid development of virtual globe technologies provides for an effective framework to efficiently demonstrate meteorological and oceanographic concepts to not only specialized weather forecasters but also to students and the general public. With their emphasis upon geolocated data, virtual globes represent the next evolution beyond the traditional web browser by allowing one to define how, where, and when various data are displayed and dynamically updated.In this article, we describe a virtual globe implementation of the NRL TC-Web satellite data processing system. The resulting NRL Tropical Cyclones on Earth (TC-Earth) application is designed to exploit the capabilities of virtual globe technology to facilitate the display, animation, and layering of multiple environmental satellite imaging and sounding sensors for effective visualization of tropical cyclone evolution. As with the NRL TC-Web, the TC-Earth application is a dynamic, realtime application, driven by the locations of active and historical tropical cyclones. TC-Earth has a simple interface that is designed around a series of placemarks that follow the storm track history. The position coordinates along the storm track are used to map-register imagery and subset other types of information, allowing the user a wide range of freedom to choose data types, overlay combinations, and animations with a minimum number of clicks. TC-Earth enables the user to quickly select and navigate to the storm of interest from the multiple TCs active at anytime around the world or to peruse data from archived storms.     

A streaming narrow-band algorithm: interactive computation and visualization of level sets

Deformable isosurfaces, implemented with level-set methods, have demonstrated a great potential in visualization and computer graphics for applications such as segmentation, surface processing, and physically-based modeling. Their usefulness has been limited, however, by their high computational cost and reliance on significant parameter tuning. This paper presents a solution to these challenges by describing graphics processor (GPU) based algorithms for solving and visualizing level-set solutions at interactive rates. The proposed solution is based on a new, streaming implementation of the narrow-band algorithm. The new algorithm packs the level-set isosurface data into 2D texture memory via a multidimensional virtual memory system. As the level set moves, this texture-based representation is dynamically updated via a novel GPU-to-CPU message passing scheme. By integrating the level-set solver with a real-time volume renderer, a user can visualize and intuitively steer the level-set surface as it evolves. We demonstrate the capabilities of this technology for interactive volume segmentation and visualization.     

Visualizing large data sets in the earth sciences

The authors describe the capabilities of McIDAS , an interactive visualization system that is vastly increasing the ability of earth scientists to manage and analyze data from remote sensing instruments and numerical simulation models. McIDAS provides animated three-dimensional images and highly interactive displays. The software can manage, analyze, and visualize large data sets that span many physical variables (such as temperature, pressure, humidity, and wind speed), as well as time and three spatial dimensions. The McIDAS system manages data from at least 100 different sources. The data management tools consist of data structures for storing different data types in files, libraries of routines for accessing these data structures, system commands for performing housekeeping functions on the data files, and reformatting programs for converting external data to the system's data structures. The McIDAS tools for three-dimensional visualization of meteorological data run on an IBM mainframe and can load up to 128-frame animation sequences into the workstations. A highly interactive version of the system can provide an interactive window into data sets containing tens of millions of points produced by numerical models and remote sensing instruments. The visualizations are being used for teaching as well as by scientists     

Multiresolution representation and visualization of volume data

A system to represent and visualize scalar volume data at multiple resolution is presented. The system is built on a multiresolution model based on tetrahedral meshes with scattered vertices that can be obtained from any initial dataset. The model is built off-line through data simplification techniques, and stored in a compact data structure that supports fast on-line access. The system supports interactive visualization of a representation at an arbitrary level of resolution through isosurface and projective methods. The user can interactively adapt the quality of visualization to requirements of a specific application task and to the performance of a specific hardware platform. Representations at different resolutions can be used together to further enhance interaction and performance through progressive and multiresolution rendering     

面向数字地球的虚拟现实系统关键技术研究

研究了面向数字地球的虚拟现实系统关键技术，提出了多层场景引擎（MLSE）、视点相关动态多分辨率地形模型（VDDMTM）和ActiveX构件网络模型。MLSE采用层机制集成多元数据，实现场景绘制和交互。VDDMTM基于四叉树表示多分辨率地形，并结合多分辨率纹理映射，根据视点位置对大规模地形实时简化，既提高了场景绘制速度，又保留了视点相关细节。网络模型采用基于Client/Server结构的ActiveX构件方案，既满足数字地球的建模特性，又支持标准的WWW浏览器。在此基础上开发了一个面向数字地球的原型系统－虚拟地球系统VES（VirtualEarthSystem），并用于虚拟永定河和喜马拉雅山。     

Scientific visualization and the Rivers Project at the NationalCenter for Supercomputing Applications

The author describes NCSA's approach to the development of visualization tools for scientists at remote locations as well as those with complex special requirements. The Rivers (Research on Interactive Visual Environments) Project is an interesting and potentially important attempt to extend high-end visualization to the interactive steering of supercomputer simulations. Other groups at NCSA deal with `routine' graphics, with custom high-quality animations for scientists, and with the development of toolsets ranging from generating color palettes to volume visualization     

The application visualization system: a computational environmentfor scientific visualization

A software system for developing interactive scientific visualization applications quickly, with a minimum of programming effort, is described. This application visualization system (AVS) is an application framework targeted at scientists and engineers. The goal of the system is to make applications that combine interactive graphics and high computational requirements easier to develop for both programmers and nonprogrammers. AVS is designed around the concept of software building blocks, or modules, which can be interconnected to form visualization applications. AVS allows flow networks of existing modules to be constructed using a direct-manipulation user interface, and it automatically generates a simple user interface to each module     

Digital preservation and dissemination of ancient lithic technology with modern micro-CT

Flaked stone tools were first made and used by early humans from at least 2.6 mya. By analysing temporal, geographical and species-specific variations in tool morphology scientists attempt to understand the evolution of cognition, culture and human behaviour. However, the dispersal of artefact collections around the globe in a large number of institutions makes direct study and comparison of the artefacts problematic, and therefore dependant on published drawings and photographs. The present study aims to determine whether CT could be used to create computerised (“virtual”) artefacts, and data shared with scientists and the public. In particular this study assesses whether CT would be cost effective and capture the fine surface topology created by the knapping process. Scanning could cost as little as €2 per flake. It was found that micro-CT could produce accurate high-resolution “virtual” artefacts that resolve features greater than 50 μm. Importantly, it was possible to visualise the key features of percussion, which distinguish intentionally made flakes from natural breakage. Furthermore, it was possible to recreate missing flakes (or parts thereof) from refitted groups of material by visualising void spaces. Hence it is possible to obtain a better understanding of the knapping process and obtain a glimpse of the flakes that were actually used as tools. The virtual flint artefacts are completely interactive and can be manipulated, viewed, measured and analysed as though they were in the hand and more useful to researchers than 2D drawings or photographs. The models are only 20 MB in size and can easily be distributed online, widening access to collections and access to physical specimens could be replaced with rapid stereotypes (3D prints). In addition, micro-CT imaging technology may give rise to new online “Virtual Museums” where digital data are shared widely and freely around the world, but the original material is conserved in mint condition, only to be removed for new or improved non-destructive imaging techniques.     

Extending interactive data language with higher-order functions

The interactive data language (IDL) is a dynamically typed array processing language widely used for the analysis of images and other scientific data. It operates in two basic modes. The first is a command line mode for interactive analysis and visualization of scientific data. The second is as a development platform for end-user applications which process scientific data. This paper details the introduction of higher-order functions to the core IDL. The purpose of these constructs is to increase the productivity of the interactive IDL user. Historically, interactive users of IDL have been scientists and engineers engaged in the exploration of new data. The addition of functional constructs aids these users by allowing them to accomplish, in a few lines of code, what might otherwise require writing a custom function which is then compiled and used. The constructs described were implemented as C language extensions to core IDL. The IDL extensions themselves are available for download at .     

Automatic camera control in virtual environments augmented using multiple sparse videos

Automated virtual camera control has been widely used in animation and interactive virtual environments. We have developed a multiple sparse camera based free view video system prototype that allows users to control the position and orientation of a virtual camera, enabling the observation of a real scene in three dimensions (3D) from any desired viewpoint. Automatic camera control can be activated to follow selected objects by the user. Our method combines a simple geometric model of the scene composed of planes (virtual environment), augmented with visual information from the cameras and pre-computed tracking information of moving targets to generate novel perspective corrected 3D views of the virtual camera and moving objects. To achieve real-time rendering performance, view-dependent textured mapped billboards are used to render the moving objects at their correct locations and foreground masks are used to remove the moving objects from the projected video streams. The current prototype runs on a PC with a common graphics card and can generate virtual 2D views from three cameras of resolution 768×576 with several moving objects at about 11 fps.     

AutoVisual: rule-based design of interactive multivariatevisualizations

An extension to the n-Vision visualization system, which provides users with a 3D virtual world within which they can visualize and manipulate representations of multivariate relations is discussed. The extension, AutoVisual, is rule based system that eliminates the difficulty in choosing among the many alternative when designing visualizations. AutoVisual designs interactive virtual worlds for visualizing and exploring multivariate relations. It is guided by user-specified visualization tasks and a rule base of design principles. AutoVisual's visualization techniques and the visualization tasks it handles are described. Example visualizations AutoVisual has generated for two problem domains are discussed