The VAPOR project is an Open Source software development effort aimed at improving the ability of researchers in the Earth and Space sciences to analyze and interpret results from some of the largest numerical simulation outputs. The genesis of this work was an NSF-ITR research grant that supported NCAR as well as collaborators at the University of California at Davis and the Ohio State University. Though VAPOR’s origins are strongly rooted in geophysical turbulence, later work on VAPOR has focused on expanding its capabilities to support the needs of the broader Earth and Space sciences communities. Development of VAPOR is guided by an international steering committee of scientists that set development priorities, dictate software requirements, and serve as friendly users for testing and evaluating new software features. VAPOR’s unique features include its use of a progressive access model that permits exploration of some of the largest simulation outputs using only desktop computing resources; a feature set and user interface that are focused on the needs of the Earth sciences communities; and a strong emphasis on supporting quantitative data analysis.
A fundamental capability, and one of the driving requirements behind much of VAPOR's design, is the ability for users to interactively explore large, time-varying, gridded data sets using only desktop (e.g commodity laptop or PC) computing resources. This feat is accomplished through the use of a progressive access data model; when selecting a variable to operate on in the VAPOR environment the user specifies not only the name of the variable, a time step, and possibly a spatial region of interest (ROI), but also provides a quality parameter. This quality parameter enables the user to trade speed for accuracy. Lower quality levels can be processed more quickly, but the resulting analysis operation, such as volume rendering, may suffer from visual artifacts. Likewise, higher quality levels will produce more accurate results, but may take longer (and require more computing resources). This model is similar to the one employed by the ubiquitous GoogleEarth; when the user is viewing an area from far above the earth a low resolution image is displayed, but as the user zooms in closer higher, and higher resolution images are used.
Unfortunately, to get the most benefit out of a progressive access data scheme requires an underlying data format that supports progressive access. Commonly used scientific data formats such as netCDF or HDF have no such provision. Hence, VAPOR provides its own scientific data format supporting progressive access, the VAPOR Data Collection (VDC). To take advantage of VAPOR's large data handling ability a data set must first be converted into a VDC. Numerous methods are available for performing this conversion and are discussed here.
VAPOR is not a general purpose visualiztion application. It is a targeted tool, aimed primarily at the specialized needs of the earth and space science communities, particularly in numerical weather prediction, numerically simulated turbulence, and ocean modeling. Though VAPOR offers many general purpose visualization algorithms such as volume rendering and isosurfaces, VAPOR also provides many features not found in more general scientific visualization packages, such as support for geo-referenced data. Another particular emphasis in VAPOR is the ability to explore time varying flow fields.
VAPOR is intended to help domain scientists explore, analyze, and interpet their gridded data sets through visualization aided analysis. VAPOR provides a rich set of powerfull, quick-look advanced 3D visualization techniques that enable a qualitative understanding of complex phenomena, and are adept at helping identify spatial or temporal regions of interest. Once an interesting region or feature is identified visually, more detailed, quantitative analysis can be performed. While VAPOR provides a degree of quantitative information, often more capable, mathematically oriented tools are needed (e.g MatLab, NumPy, or IDL). In this case VAPOR can help focus the direction of these more quantitatively-oriented tools.
VAPOR is not a single application, but a collection of tools, libraries, example scripts, and sample data sets. The most visible component of the VAPOR suite is the Graphical User Interface, vaporgui. Vaporgui is a desktop application that can be run on Linux, Windows, and Mac OS systems. Throughout the VAPOR documentation the terms VAPOR and vaporgui are often used synonymously. VAPOR also contains numerous UNIX command line utilities for processing data, most of which are used to convert foreign data formats into the aforementioned VDC.
Numerous sources of help are available for VAPOR. These include: