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How Google Earth Images Are Made
An anonymous reader writes "The Google Librarian Central site has up a piece by Mark Aubin, a Software Engineer who works on Google Earth. Aubin explains some of the process behind capturing satellite imagery for use with the product. 'Most people are surprised to learn that we have more than one source for our imagery. We collect it via airplane and satellite, but 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. As the plane takes a predefined route over the desired area, it forms a series of parallel lines with about 40 percent overlap between lines and 60 percent overlap in the direction of flight. This overlap of images is what provides us with enough detail to remove distortions caused by the varying shape of the Earth's surface.'
Maybe you should download and try Google Earth which....
requires 3D hardware, can do smooth zooms, tilts, and pans, and showa the world with elevation.
Google Earth IS the evolved version of the Keyhole client you referred to.
Actually there's no need for a camera's "panoramic" mode any more. Check out Autostitch , a free for personal use program created by researchers at UBC. Essentially you take as many pictures as you want with varying amount of overlap. Each picture can be rotated differently and even vary somewhat in exposure, and this program automatically figures out which ones go where, even throwing out ones that are not part of the scene. It takes a ton of ram and some CPU speed but the result is better than any other method I've seen. Some examples here at the bottom of this page: AZ Snow Pictures.
Unfortunately, when working with that kind of imagery collection the high tech part is on the processing end.
You need to:
1. Correct for lens distortion
2. Correct for tilt
3. Correct for terrain distortion
4. Correct lighting imbalances across the scene
5. Assign it bounding coordinates of a known mapping coordinate system / projection
This is the basic process for making an orthophoto. These are generally dealt with using a software package like Erdas Imagine which can deal with all the steps in one swoop. It looks at the lens info, coordinate tie down points, an elevation model and outputs a photo that can be used for linear measurements.
So anyway, it is possible to accurately georeference many sources of imagery, it just depends how much time you want to spend processing it. If you plan on covering a large area, taking photos out of the window of a Cessna is probably not the best way.