Image flight
As aerial survey in which it is Geodesy and Photogrammetry the strip-shaped flying off of areas for the production of terrain models or maps referred. A special measuring camera is mounted on the underside of the aircraft , which takes vertical aerial photos at fixed intervals .
With the classic serial camera , the shutter is automatically triggered by an overlap regulator, whereby the longitudinal overlap is usually 60 percent. This coverage area can then be evaluated by means of stereo photogrammetry for each successive pair of images. Newer systems regulate the coverage through a combination of flight navigation, altitude measurement over the ground and GPS route measurement.
Usually the area is flown over in the form of a rectangular block of images, which in addition to the above. Longitudinal overlap also requires sufficient transverse overlap of the individual image strips - flown in opposite directions - of 20 to 25%. In this way, the recorded area is gradually covered in a meandering shape and every point on the ground appears on several images. In the subsequent evaluation , the overflown area is transformed into the coordinate system of the national survey using terrestrially measured control points .
As an alternative to image blocks, digital line sensors are used today , which scan the terrain line by line across the direction of flight. The stereo effect is achieved by the system recording strips in multiple directions (e.g. front and back) at the same time. This also ensures that each point on the ground appears two or three times in the images.
The forerunner of surveying with aerial photographs is terrestrial photogrammetry , in which two or more measurement images recorded on the earth's surface are evaluated.