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Google Charts JSON Data Tables directly from ERDDAP
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  • Roland Schweitzer,
  • Robert Simons,
  • Kevin O'Brien,
  • Eugene Burger
Roland Schweitzer
Weathertop Consulting, LLC

Corresponding Author:roland.schweitzer@noaa.gov

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Robert Simons
NOAA Pacific Grove
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Kevin O'Brien
Joint Institute for the Study of the Atmosphere and Ocean
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Eugene Burger
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ERDDAP is a data server developed at NOAA Southwest Fisheries Science Center that allows users to easily access and download subsets of gridded and tabular data. At the Scientific Data Integration Group at NOAA’s Pacific Marine Environmental Laboratory we have focused on ERDDAP as the primary mechanism by which we serve all of our tabular data. Besides offering data access in a variety of useful formats, ERDDAP takes care of normalizing the data structure so that all tabular data sets have a simple row and column structure. Additionally, time values are normalized to have a consistent units across all data sets on the server. The simplified tabular nature of the discrete data in ERDDAP lends itself nicely to use with the Google Visualization API (Google Charts). Charts is an API which renders nearly all of the graphics in the browser client. The basis of all charts is the Google Charts DataTable which is exactly analogous to a TableDap table in ERDDAP. Charts are interactive, visually pleasing, free and easy to use and so connecting ERDDAP data to Google Charts is a natural fit. Even though ERDDAP has many output formats including several different JSON renderings, none fit exactly into the specified Charts data types. Initially, as a result, it was necessary to create custom code (either in the client or on a server between the client and the ERDDAP server) to manipulate the ERDDAP data stream to match the Charts API requirements. However, since Charts has a well-documented specification for a JSON representation of the required data type and because ERDDAP is an open source project, it was possible to extend ERDDAP to support the Charts DataTable as a new data type. Using this new data type, it’s possible to instantiate a Charts DataTable object directly from the ERDDAP URL using a simple Ajax call in the client which downloads the JSON DataTable representation. Because the newly added data type is now native to ERDDAP, it is possible to use default constraint syntax and ERDDAP RESTful services (using the ERDDAP user interface if desired) to build the URL for the exact data subset which is to be visualized by the desired google chart. In this presentation, we’ll explain what we’ve done to add the JSON data type to ERDDAP and provide many examples of client-side rendering of earth science and engineering data using Google Charts directly from ERDDAP URLs.