No. 33 October 1995

The Program for Climate Model Diagnosis and Intercomparison has developed the Visualization and Computation System (VCS) computer software for the selection, manipulation, and display of scientific data. By specification of the desired data, the graphics method, and the display template, the VCS user gains virtually complete control of the appearance of the data display and associated text and animation. In addition to operating in a fully interactive mode, the user can run VCS from a script file, or can alternate between interactive and script modes.

The Visualization and Computation System (VCS)
Uniquely Versatile Software

Dean N. Williams, Robert L. Mobley, Robert S. Drach, and Thomas J. Phillips
Lawrence Livermore National Laboratory

The principal mission of the Program for Climate Model Diagnosis and Intercomparison (PCMDI) is to develop improved methods for the diagnosis, validation, and intercomparison of global climate models. The need for such standards has become increasingly apparent as more complex climate models are developed, while the disagreement among models, and between models and observations, remains significant and poorly documented. The nature and causes of these disagreements must be better understood before these models can be confidently used for climate sensitivity and predictability studies in support of global change research.

The massive amounts (~ gigabytes) of data produced by climate model simulations make imperative the development of powerful visualization tools. Because no single display technique can elucidate all facets of climate model behavior, the visualization system must possess a wide range of graphic capabilities. In comparing simulations from many different models, it is also necessary to perform grid transformations and computations of additional diagnostic variables.

The PCMDI Visualization and Computation System (VCS) is expressly designed to meet these needs of climate scientists. Because of the breadth of its capabilities, VCS can be a useful tool for other scientific applications as well. VCS allows wide-ranging changes to be made to the data display, provides for hardcopy output,and includes a means for recovery of a previous display. VCS also allows the user to browse large amounts of data and obviates the need to create intermediate data files.

In the VCS model (Williams and Mobley 1994), the data display is defined by a trio of named attribute sets, designated the "primary elements." These include: the data, which define what is to be displayed; the graphics method, which specifies the display technique; and the picture template, which determines the appearance of each segment of the display (Fig. 1).

Fig. 1. Diagram of the VCS model and capabilities.
(Generated with help from Chris L. Anderson,
National Energy Research Supercomputer Center.)

Panels for manipulating these primary elements are color-coded in the VCS interface: attributes associated with the data are represented in red, those with the graphics method in blue, and those with the picture template in green (Fig. 2).

Fig. 2. The VCS interface, with a display of January mean sea
level pressure simulated by the European Centre for Medium-Range
Weather Forecasts (ECMWF) model.

In addition, detailed specification of the primary elements' attributes is provided by eight "secondary elements":

By combining primary and secondary elements in various ways, the VCS user can comprehensively diagnose and intercompare climate model simulations. VCS provides capabilities to:

Procedures for exercising these capabilities are documented online in VCS (Williams et al. 1995). Especially noteworthy features of VCS are its data representation model and its scripting, computational, and animation capabilities.

Data representation in VCS is transparent to the user. Data file formats presently accessible by VCS include: the Data Retrieval and Storage (DRS) format, developed by PCMDI (Drach and Mobley 1994; software is available via anonymous FTP site in directory /pub/drs); the Network Common Data Form (netCDF) format, developed by the Unidata program of the National Science Foundation (NSF) Division of the Atmospheric Sciences (available via FTP site in directory /pub/netcdf); and formats supported by the Grid Analysis and Display System (GrADS), developed by the Center for Ocean-Land-Atmosphere Studies (COLA) (available via FTP site Within VCS, the user can browse data directories and read variables from combinations of files, perform grid transformations, and compute new variables. A data array's dimensions can be transposed, reversed, sub-selected, randomly selected, and wrapped. The attributes of the dimensions, as well as those of the array data variable, can be modified.

The scripting capability of VCS serves many purposes. It allows the user to save the system state for replay in a later session; to save primary and secondary element attributes for use in later visual presentations; to save a sequence of interactive operations for replay; and to recover from a system failure.

New diagnostic variables can readily be computed in VCS by building mathematical expressions from basic operators and functions. Arithmetic and exponential operators, and functions for computing the statistical mean and standard deviation of a data variable are presently available.

The VCS animation capability allows three-dimensional visualization of one or more data variables (e.g., the temporal progression of a two-dimensional field). The animation control panel creates sequences of raster images that may be stored in memory or in an output file; their animation then can be viewed subject to user control. Other VCS animation options include the ability to modify the colormap, to change the direction of the flow, to view each frame in time-delay mode, and to pan or zoom all while the animation is proceeding.

In the future, PCMDI will continue to enhance the capabilities of VCS. Development priorities include provision of the ability to access data via directories or a database, as well as data written in the Hierarchical Data Format (HDF); to save data in HDF-, netCDF-, and GrADS-formatted files; to increase the computational power of VCS; and to augment the types of available graphics methods.

Availability of VCS

VCS is operable on the following computing platforms: Sun, running operating systems SunOS 4.1.3 or Solaris 2.4; Silicon Graphics Incorporated (SGI), running operating systems IRIX 5.2 or 5.3; and Hewlett Packard (HP), running operating system HP-UX 9.0.5. Because VCS is written in ANSI C and utilizes X/Motif, the software should compile on other UNIX-based platforms as well.

VCS is available free of charge to users in nonprofit institutions who sign a PCMDI collaborative agreement stipulating that the software will not be sold to third parties. To obtain a copy of this agreement, contact Dean N. Williams (


Drach, R. S., and R. L. Mobley. 1994. The DRS user's guide. PCMDI Report No. 16, Lawrence Livermore National Laboratory, Livermore, California. 50 pp.

Williams, D. N., and R. L. Mobley. 1994. The PCMDI Visualization and Computation System (VCS): A workbench for climate data display and analysis. PCMDI Report No. 17, Lawrence Livermore National Laboratory, Livermore, California. 104 pp.

Williams, D. N., R. L. Mobley, R. S. Drach, and T. J. Phillips. 1995. Hints and examples for the use of the PCMDI Visualization and Computation System (VCS). PCMDI Report No. 23, Lawrence Livermore National Laboratory, Livermore, California. 85 pp.


Dean N. Williams
Program for Climate Model Diagnosis and Intercomparison
Lawrence Livermore National Laboratory
Livermore, California 94550
(510) 423-0145
FAX (510) 422-7675

Robert S. Drach
Program for Climate Model Diagnosis and Intercomparison
Lawrence Livermore National Laboratory
Livermore, California 94550
(510) 422-6512
FAX (510) 422-7675

Program Manager

Michael R. Riches
Office of Health and Environmental Research
ER-74, U.S. Department of Energy
Washington, D.C. 20585
(301) 903-3264
FAX (301) 903-8519

Prepared by the Carbon Dioxide Information Analysis Center, OAK RIDGE NATIONAL LABORATORY, Oak Ridge, Tennessee 37831-6335 managed by LOCKHEED MARTIN ENERGY RESEARCH CORP. for the U.S. DEPARTMENT OF ENERGY under contract DE-AC05-96OR22464.

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This electronic document was prepared by Sonja Jones, CDIAC. (9/6/96)