Government Computer News
Cutting Edge: NOAA builds AJAX-based data viewer
The National Oceanic and Atmospheric Administration’s Pacific Marine Environmental Laboratory has released a browser-based application called the Dapper Data Viewer for viewing oceanographic and atmospheric data.
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DChart, as it is also known, enjoys a particularly rich feature-set, thanks to the use of an emerging Web application technology called Asynchronous JavaScript and XML (AJAX).
Pacific Marine Environmental Laboratory (PMEL) developer Joe Sirott created DChart with help of other staffers so users could visualize in-situ oceanographic or atmospheric data, a particularly challenging type of data to render in graphical format. The software was first released in December; an updated version was released last month.
A technology generating buzz in the Web application development community, AJAX allows developers to build Web applications that enjoy at least some of the functionality usually found only in desktop programs.
Although Sirott has learned about some of the limits of AJAX, the approach nonetheless provided the needed functionality for the complex requirements of DChart.
The Seattle-based PMEL hosts a wide collection of global weather station readings of temperature, air pressure, wind and other variables. To offer this data to scientists, the NOAA laboratory deploys the open source Network Data Access Protocol (OpenDap), server software widely used in the geoscience community. OpenDap allows users to download only the specific data needed at the time, rather than the entire dataset, conserving resources of server and client alike.
Before DChart was released, scientific users had little in the way of software for actually viewing the data in a visual form. “While there are many client programs for OpenDap-gridded data, there aren’t that many programs that support OpenDap in-situ data,” Sirott explained.
Gridded data is usually formatted in a uniformly spaced, four-dimensional framework with dimensions representing latitude, longitude, depth or height and time. In contrast, in-situ data “contains measurements of variables at irregular latitude/longitude/depth/time points,” Sirott explained.
With DChart, a user selects one or more stations and then plots the data created at those stations. The program smoothes the herky-jerky nature that hampers most map-based Web sites. Users can interact with the map without having the entire page redrawn. They can also zoom in or out, or drag different parts of the map into the viewing area. A list of the variables “changes dynamically as the user selects different datasets,” Sirott said.
To develop the program, Sirott first looked at using Macromedia Flash from Adobe Systems Inc. of Mountain View, Calif. He didn’t want to lock the application into a vendor-specific language (ActionScript), nor did he wish to rely on a client plug-in, which Flash requires. He also considered using Java applets, though was discouraged by the sluggishness that usually comes with initializing the Java Virtual Machine on the user’s machine.
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