Visualizing dynamic geosciences phenomena using an octree-based view-dependent LOD strategy within virtual globes
Introduction
The “Digital Earth” concept was first proposed by the former U.S. Vice President Albert A. Gore, Jr., in 1998. The concept refers to “a multiresolution, three-dimensional representation” of the Earth, through which scientists and the general public can develop a better understanding of various physical phenomena on the planet (Gore, 1998). To support the development of the Digital Earth, different geovisualization platforms, such as World Wind by NASA, have been developed based on the virtual globe concept. Researchers utilize these virtual globes to visualize a broad range of geospatial datasets to support spatial analysis, knowledge mining, and decision making (e.g., Butler, 2006, Webley et al., 2009, Wu et al., 2010). The graphical representations of these datasets and the tools provided in these visualization platforms help users discover patterns in the data, formulate hypotheses to be tested, and develop a better understanding of the processes under investigation.
While visualization techniques have the potential to reveal patterns and uncover knowledge hidden behind the complex and/or large volume of geospatial data, the use of these techniques is encountered with some impediments. Gahegan (1999) identifies several typical challenges in geovisualization such as representing natural phenomena in a multidimensional space and organizing geospatial data efficiently to improve visualization performance despite increasing data volume. New visualization techniques and schema are constantly needed to handle the increasing volume of geospatial data.
More technical challenges arise when providing multidimensional visualization capabilities over the Internet. In the Internet environment, datasets from different sources are processed in the same visualization environment. Synchronization of retrieval, processing (e.g., reprojection), and rendering in a collaborative environment is critical to performance. The capabilities of the clients, especially their hardware configurations, may vary. Techniques such as hardware acceleration may not be applicable to all clients. In addition, visualization performance is constrained by the implementation environment and visualization platform adopted. Visualization platforms developed in Java are usually not as efficient as those in C/C++ because of the limitations of the Java virtual machine.
The current study addresses some of the challenges in visualizing dynamic geosciences phenomena represented by complex data in an Internet environment. This study has three main objectives: (1) to develop a systematic framework to visualize multidimensional data in an Internet-based virtual globe platform; (2) to develop a data structure to accommodate dynamic volumetric visualization; an octree-based efficient data structure is adopted to tackle this data complexity issue; and (3) to address the visualization performance issue using a level of detail (LOD) strategy. This method is expected to support and enhance the visualization of a large volume of dynamic volumetric geospatial data in virtual globe environments.
The remainder of the paper is organized as follows. Section 2 provides a focused review of previous studies on visualizing 3D/4D geospatial data in an Internet environment. Section 3 describes our approach to organize and render dynamic volumetric data in virtual globes. Section 4 demonstrates the proposed approach using simulated dust storm data. The performances of visualization with and without our proposed strategy are experimented and compared. Section 5 concludes and discusses future directions.
Section snippets
Related work
Due to the advancement of data collection technologies, data in 3D with and without the temporal dimension have become abundantly available in the areas of geosciences and environmental science (Engel-Cox et al., 2004, Kelley et al., 2004). Computational and numerical models also simulate the dynamics of many physical phenomena in a 3D space (e.g., Shen et al., 2006, for dynamic geosciences phenomena). While novel visualization platforms such as virtual globes could be regarded as a logical
Data
In this paper, volumetric data simulating geosciences phenomena are expressed in 3D matrices. In such a structured matrix, each element represents the attribute value at the linear-encoded location. For example,
In Eq. (1), pijk is the attribute value of the phenomenon in the 3D space at (xi, yj, zk). The attribute may represent, for instance, the air pressure at a certain height over a location. The terms xi, yj, and zk are defined as follows: xi=x0+iΔ
An illustrative example
To demonstrate the proposed 3D/4D visualization framework, we use data simulating a dust storm event occurring in the southwestern United States in 2008. The data stored in NetCDF format are hourly dust particle densities generated by the Nonhydrostatic Mesoscale dust Model (NMM-dust) (Xie et al., 2010). The simulation replicates a storm event from 12:01 am on January 7, 2008 to 11:59 pm on January 8, 2008, producing data for the 48-h period. The geographic coverage of the data is from 25.56°N
Conclusions and future work
The objective of this paper is to propose a systematic framework for rendering large-scale geosciences phenomena in virtual globes. A multiresolution octree data organization method with a view-dependent continuous LOD rendering strategy is implemented. The original volumetric dataset is organized into an octree structure so that the efficiency to access 3D/4D geospatial data is improved. Exploiting the structure and organization of this data model, the view-dependent LOD was configured to
References (37)
- et al.
Qualitative and quantitative evaluation of MODIS satellite sensor data for regional and urban scale air quality
Atmospheric Environment
(2004) Geometric modeling using octree encoding
Computer Graphics and Image Processing
(1982)- et al.
A virtual globe-based 3D visualization and interactive framework for public participation in urban planning processes
Computer, Environment and Urban System
(2010) - et al.
High-performance computing for the simulation of dust storms
Computers, Environment and Urban Systems
(2010) - et al.
Large-scale data visualization using parallel data streaming
IEEE Computer Graphics and Applications
(2001) - Bai, Y., Han, X., Prince, J., 2007. Octree grid topology preserving geometric deformable model for three-dimensional...
- et al.
Multiresolution volume visualization with a texture-based octree
The Visual Computer
(2001) Virtual globe: the Web-wide world
Nature
(2006)- Clasen, M., Hege, H.-C, 2006. Terrain rendering using spherical clipmaps. In: Ertl, T., Joy, K., Santos, B., (Eds.),...
- Funkhouser, T., Séquin, C., 1993. Adaptive display algorithm for interactive frame rates during visualization of...
Four barriers to the development of effective exploratory visualisation tools for the geosciences
International Journal of Geographical Information Science
Digital Earth: Understanding Our Planet in the 21st Century
Interactive visualization of earth and space science computations
Computer
Tall precipitation cells in tropical cyclone eyewalls are associated with tropical cyclone intensification
Geophysical Research Letters
Volume rendering: display of surfaces from volume data
IEEE Computer Graphics and Applications
Level of Detail for 3D Graphics
Cited by (35)
Real-time switching and visualization of logging attributes based on subspace learning
2021, Computers and GeosciencesIntegrated multi-scale reservoir data representation and indexing for reservoir data management and characterization
2020, Computers and GeosciencesCitation Excerpt :It is often combined with the LOD technique to create 3D representations of object surfaces and buildings (Jiang et al., 2012; Melero et al., 2008). In addition to representing features at different scales, octree can also organize attribute data of different resolutions; a typical example is spatial resampling-based pyramid models for organizing massive multi-resolution attribute data (Bai et al., 2014; Li et al., 2011). Bai(2014) presented an octree method to construct and display a multi-scale geologic model effectively; however, in the process of upscaling the strata and the fault, the method merges fixed-eight neighboring grids into one without considering the unfixed proportional relationship between strata at different scales, which will cause a high error in the fault location.
A tile service-driven architecture for online climate analysis with an application to estimation of ocean carbon flux
2019, Environmental Modelling and SoftwareAn efficient dynamic volume rendering for large-scale meteorological data in a virtual globe
2019, Computers and Geosciences