Aerial photo measurement

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The aerial photograph measurement (also aerophotogrammetry or aerial photograph photogrammetry ) is the most important group of methods of photogrammetry .

The measurement of objects of the earth's surface by means of measurement images , the two or more camera -Standpunkten in the air (balloon image flight ) can be made. As a rule, a measuring aircraft flies across the terrain in strips and the measuring camera is automatically triggered in such a way that two consecutive images overlap by about 60%. This coverage area can then be evaluated for each " image pair " by means of stereo photogrammetry.

The terrain is usually flown over in the form of a rectangular block of images, which, in addition to the above-mentioned longitudinal overlap, also requires a sufficient transverse overlap of the individual flight strips of around 20-25%. In this way, the recorded terrain is gradually covered in a meandering shape and can be transformed into the coordinate system of the national survey during the subsequent evaluation using terrestrially measured control points . The number of necessary control points can be reduced by recording the exact flight path using GPS or inertial navigation and reinforcing it with bundle block adjustment .

As an alternative to image blocks, digital sensors are used today, which record the terrain line by line in the direction of flight, comparable to a flatbed scanner (so-called line sensors ). In this case, there is a single image strip per airline. The stereo effect is achieved by the fact that the camera simultaneously records stripes in several directions (typically forwards, downwards and backwards). This also ensures that each point on the ground appears two or three times in the images.

The analogue of aerial photo measurement is the earth image measurement , which today is mostly referred to as terrestrial photogrammetry.

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