IDENTIFICATION OF EXISTING VISUALIZATION PACKAGES RELEVANT TO THE ESMF USER COMMUNITY
May 1, 2003Randall A. Jones, GST
James W. Williams, GST
The Earth System Modeling Framework (ESMF) is a collaboration of Earth scientists and computational experts from major U.S. Earth modeling centers to develop a robust, flexible set of software tools to enhance ease of use, performance portability, interoperability, and reuse in climate, numerical weather prediction, and data assimilation applications. [1]
Creating a comprehensive global modeling system or Earth System Model (ESM) [2] presents the need for scientific analysis and visualization tools to work with the large amounts of resulting data. This presents the need for visual exploration of ESMF outputs as well as accurate analysis and high-quality visual presentation of discovered data. In order to fill this need, it is necessary to identify existing interactive, high-end visualization packages relavant to the ESMF user community.
Candidate Criteria
An extensive list of criteria was used to determine the capability of packages relevant to the requirements for ESM visualization.
- cross-platform (Mac OS X, Linux, IRIX, Solaris, Unix, MS Windows)
- open-source model, freely available world-wide
- accessible through a library for application development
- support a common, accepted scripting language
- support for irregular grids: rectilinear, curvilinear
- support for time-varying 2D and 3D datasets with several scalar and vector variables
- support simultaneous visualization of multiple grids of different scales or topologies
- community support, project activity
- interactive and graphical output including:
- 2D contours
- 3D surfaces
- surface texture/coloring
- 3D volume rendering
- slicing
- particle trace, streamlines
- vector visual representation
- presentation quality image output (vector PS, print resolution image)
- animation (sequential frame output and/or direct animation or movie creation)
- scene output for high-quality rendering (RenderMan, POVRay, Tachyon)
It is essential that an analysis and visualization tool have the ability to read and operate on native ESM grid data types, data file formats and meta-data without conversion to an intermediate data format and without grid interpolation.
It is intended that a resulting comprehensive analysis and visualization package run on modern commodity desktop computing hardware.
This report is intended to be an overview of general visualization capabilities and does not address specific details of ESM analysis. The following packages were considered as candidates for ESMF visualization: AVS, OpenDX, GrADS, IDL, NCAR Graphics, VTK, Vis5D, VisAD. Two specific candidates, VTK and OpenDX, have been identified which meet the outlined ESM criteria for visualization. These packages provide general-purpose visualization capabilities on which comprehensive visualization and analysis tools can be based.
VTK
The Visualization ToolKit (VTK) is a freely available, open source software system for 3D computer graphics, image processing and visualization that meets all of the stated ESM criteria. In addition to being object-oriented, all of the VTK modules are available through a scripting language interface.
"Toolkits enable complex applications to be built from small pieces. The key here is that the pieces must be well defined with simple interfaces. In this way they can be readily assembled into larger systems." [7]
"The [VTK] model is based on the data-flow paradigm adopted by many commercial systems. In this paradigm, modules are connected together into a network. The modules perform algorithmic operations on data as it flows through the network. The exectution of this visualization network is controlled in response to demands for data (demand-driven) or in response to user input (event-driven). The appeal of this model is that it is flexible, and can be quickly adapted to different data types or new algorithmic implementations." [7]
OpenDX
The OpenDX visualization package is based on IBM's Visualization Data Explorer, which IBM released as an open source package in 1999. OpenDX is a general purpose visualization system capable of visualizing many different sorts of complex datasets, including unstructured grids that meets all of the stated ESM criteria. It is based on an object-oriented visual programming model front end, interfaced to a powerful scripting language back end. The scripting language can also be used directly for batch processing. In its interactive mode, OpenDX supports browsing through datasets in interactive windows.
One of the highlights of OpenDX is its "Visual Programming Environment." This highlight is of little importance for a comprehensive ESM analysis and visualization tool due to the level of complexity that would be required to build an ESM application. OpenDX was designed as a general tool for complex visualization tasks. While it provides a library interface to the individual visualization components, this is not its strongest area.
Summary
There is no single application that will fulfill the needs of Earth system science research analysis and visualization. Instead, a collection of applications or toolkits will be needed to form the basis of a comprehensive software application.
VTK and OpenDX "are both general purpose tools... General purpose tools typically are more powerful because they are not specialized to meet the requirements of a specific model or type of realization." [6]
Both VTK and OpenDX can independently provide a generally complete set of capabilities for the visualization component of an ESM analysis and visualization application. No specialized hardware systems are necessary to achive a comprehensive analysis system.
VTK has a simple and consistent interface providing object-oriented building blocks for visualization application development. VTK provides a comprehensive collection of capabilities relevant to the visualization needs of ESMF outputs.
OpenDX provides a comprehensive interface for building visualzation applications. OpenDX is more complicated in terms of stand-alone application development. Although OpenDX has the added benefit of a general user interface in its "Visual Programming Environment," it is not clear this would be a benefit for this ESM target application.
To achieve a full-featured ESMF analysis and visualization package, significant software development effort and expertise in visualization and Earth system computational science will be necessary. Therefore, close cooperation between software developers and scientists in the ESM community will be essential in the creation of a useful application.
Processing and visualization of Earth system data must be recognized as a challenging engineering problem similar to the construction of a sophisticated scientific instrument. [2] The visualization interface or toolkit is only one piece of this "instrument."
References
- The Earth System Modeling Framework (ESMF), http://www.esmf.ucar.edu
- Hibbard, W., ACM "Computer Graphics," Vol. 36, Num. 4, Nov. 2002, pp. 5-9.
- The Visualization ToolKit, http://www.kitware.com/vtk/index.html
- OpenDX, http://www.opendx.org
- PRISM Workpackage 4a: "Development of Data Generation, Diagnostics and Visualization Tools,"
- PRISM Workpackage 4a: "High-End Graphics Packages Review,"
- Visualization '96 Proceedings, "The design and implementation of an object-oriented toolkit for 3D graphics and visualization," Oct. 1996, pp 93-100.
