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Thursday, November 16
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Posted by Harish on Thursday, November 16, 2006
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Ever wonder why are some parts of the globe blurry, and others crystal clear? Where do Google get their imagery? And how often do they update their image database?
Here is Mark Aubin, one of the founders of Keyhole, which eventually became Google Earth explaining how this is done.
Google collects image information via airplane and satellites, also just about any way you can imagine getting a camera above the Earth's surface: hot air balloons, model airplanes, even kites. The traditional aerial survey involves mounting a special gyroscopic, stabilized camera in the belly of an airplane and flying it at an elevation of between 15,000 feet and 30,000 feet, depending on the resolution of imagery you're interested in. The movement of the airplane is choreographed to collect enough detail to remove distortions caused by the varying shape of the Earth's surface.
The digital imagery is put through a series of stages such as color balancing and warping to produce the final mosaic for the entire area.
Google then adds layers of information, things like country and state borders and the names of roads, schools, and parks to make it more useful. This information comes from multiple sources: commercial providers, local government agencies, public domain collections, private individuals, national and even international governments.
Google Earth maintains hundreds of terabytes of geographic data, and is continuously updated. The images that we see might have been taken sometime in the last three years.
Source: http://www.google.com/librariancenter/articles/0604_01.html
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