Because of our broad knowledge in building web applications, AIS decided to develop a prototype that highlights the features and capabilities of open standards for geospatial processing and data sharing through web applications.

We chose the Visible Infrared Imaging Radiometer Suite (VIIRS) as our data source for the demonstration. VIIRS collects visible and infrared imagery and radiometric data for civil and military Earth monitoring. (The Day/Night Band (DNB) datasets available from NOAA’s Comprehensive Large Array-Data Stewardship System are not quite in the format we need for our application, since they are sensor data records stored within an HDF5 container.)

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Swiss army knife

Here at AIS, we’ve found Windows Azure Blob Storage to be an inexpensive, fast hosting solution for non-text or server-side loaded resources. But what if we want to use client-side JavaScript to load HTML fragments or JSON data directly from blobs? Under normal circumstances this is prevented by JavaScript’s Same Origin Policy; that is, you can’t load HTML fragments or JSON from another domain, subdomain, port or protocol.

One commonly used solution to this restriction is JSONP, but this is not available with Azure Blob Storage. Another modern option is Cross-Origin Resource Sharing (CORS), but it is also unavailable on Azure Blob Storage and not supported in some legacy browsers.

We could consider a server-side solution, such as employing an Azure Web Role to read text-based content from blob storage and serve it up from the original server. But this approach can be both wasteful and performance inhibiting.

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