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When people test cameras and lenses for resolution, they commonly use special resolution test charts that are filled with black bars of varying lengths and thicknesses. They’re kind of like eye charts, except for cameras instead of eyeballs, and with lines instead of letters.
Well, did you know that in dozens of locations around the United States, there are gigantic resolution test charts on the ground?
The Center for Land Use Interpretation writes that the strange “land-based two-dimensional optical artifacts” are used for the development of aerial photography — cameras built into airplanes and drones.
The resolution charts were mostly used during the 50s and 60s, but some of them may still be used nowadays to calibrate “flying cameras.” They have dimensions of around 50-80 feet and are coated in heavy black and white paint.
Camera-equipped aerial vehicles can fly over the giant charts and use them to test, calibrate, and focus their cameras while traveling at various altitudes and speeds. Even satellites can utilize the charts.