Evaluation device
As evaluators devices are referred to record the data and are able to analyze the data, prepare, store or forward. Which of these tasks is actually assigned to a device depends on the intended areas of application.
Nowadays, evaluation devices are mostly devices that process digital data and whose complexity often approaches that of computers. An evaluation device can receive the input through sensors or through inputs from human users.
Areas of application for evaluation devices are mainly found in automation technology , chemistry and photogrammetry.
Evaluation devices in photogrammetry
In photogrammetry , an evaluation device is a stationary measuring instrument in which two measurement images are clamped to determine the shape and position of the photographed objects.
The images are viewed through weakly magnifying measuring microscopes that have one or more line marks in the center of the field of view . By hand or foot-controlled movement of the images, the beam path that prevailed when recording pairs of images is reconstructed and then the rays are cut to the detail points to be recorded. This is how you get the coordinate differences to the camera position and the coordinates of the measuring points in the Gauß-Krüger system of national surveying.
When aligning the image pairs, some optical conditions must be met, e.g. B. the position of the main point of the image and the sharpness of the image (see Scheimpflug condition ).
Until around 1980, analog evaluation devices predominated, in which a high-precision, approximately 50 cm long stainless steel rod represented a movable measuring beam for each image . Where the two rods intersected (in the extension) was the true-to-scale position of the point that the evaluator aimed at with the line mark in both eyepieces at the same time . It could be drawn (mapped) directly with a pen .
Well-known instruments were the A7 and B8 stereo autographs from Wild Heerbrugg (now Leica Geosystems ) and similar devices from Kern Aarau . Depending on their accuracy and mechanics, they had a size that varied between double and half the desk size.
Today the analytical evaluation devices predominate, in which the beam path is no longer reconstructed by mechanically executed guide rods, but computer-controlled. As a result, the measuring instruments are smaller, require less maintenance and enable automatic data flow .
Satellite geodesy
In the first two decades of satellite geodesy , these photogrammetric instruments were also used to evaluate photo plates , with which numerous ground stations were linked by precise satellite triangulation . Special methods of equalization calculation have been developed for the calculation of high-precision coordinates of these stations . Project teams at the Graz University of Technology , the University of Bonn and the Technical University of Munich , where the evaluation centers of the European WEST project were located, were primarily responsible for the line marks recorded against the star background . The measuring accuracy increased from about 5 " to better than 1", the 2000 km European network from about 20 m to a few meters.
After 1980 the photographic measuring methods were gradually replaced by CCD sensors or laser satellites and radio processes such as GPS . If the satellite orbits are precisely known, the evaluation is partially online and reaches a few cm to mm regionally, while offline (subsequent analysis) the same accuracy is also possible globally .