| A series of landing information of helicopter, include weather influence, pilot influence, ship movement influence and so on, were reflected by landing position. So it is important to analysis how and why they influence helicopter landing, that measure the drop-position.At present, the landing position of helicopter is measured by the method of eye-measurement, which has a low precision and a bad measurement environment. It is emergent to find a new method to replace it. At recent years, the close-range photogrammetric technology is widely used in many fields as a non-contact and high-accuracy method of measurement. At the same time, technology of computer pattern recognition had greatly developed. In this paper, based on the close-range photogrammetric technology and computer pattern recognition, a new method of automatic measurement for the landing position of helicopter is proposed so as to achieve a high precision and a good measurement environment.The main work and the results obtained are as follows.(1) The basic theory of the close-range photogrammetric technology is studied, including its co-linearity equation and the method of Direct Linear Transformation. The general method of the technology was analyzed and its geometric model is built up. The error had been theoretical and experimental analyzed, an error model had been built. A co-linearity equation include error was constructed.(2) Based on the theoretical research, some contrast experiments researches were done to find the factors affecting the precision of the measurement. Shot direction was investigate, it was found that uprightness direction had a better precision; the height of shot position was investigated and found that the precision of height measurement increased with the relative height of the measured point drop; the influence of stand points'number was also investigated, it would be stable while the number up to12; measure precision of measure point in demarcated area was better than the out; image resolution should be chosen under the condition that stand point could be recognized; it had found that the error of stand point would be transmitted to the measure result.(3) Based on the plane measurement and the geometric model, an iterative algorithm of the cylinder measurement is proposed. It was built that the mathematic model of cylinder measurement; it was confirmed that demarcated algorithm of cylinder measurement. It was put forward that an iterative algorithm of coordinate z and two determine criterions of the end of iterative. Those made the measurement of cylinder as convenient and precise as the plane's.(4) Base on the analysis of photo of measure spot, fuzzy pattern recognition was used to recognize the main wheel of helicopter. It was introduced that maximum membership principle and approaching principle. Methods of pattern construct and pattern recognition was illustrated, according to the color of main wheel tire. Program flow chart was given.(5) A measurement software system was built up to measure the landing position of helicopter with VC++ and Matlab. A measurement hardware system also was built. They all were used in spot to measure the drop point of helicopter. The measurement results were compared with that of eye-measurement, and the source of error was analyzed.The analytical and the experimental results indicate that the application of the close-range photogrammetric and pattern recognition technology into measuring the landing position of helicopter could not only get a high precision but also improve greatly the measurement environment and the automation level.
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