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Measuring of railway structure clearances is a very practical issue, and the operation itself is performed all over the world using various measuring systems. The measurement is aimed chiefly at determining the limits of space that no structure (e.g. a building) located close to the railway track may cross. This paper provides a review of measurement systems used to determine clearance limits of railway buildings. Systems currently in use are based mainly on three groups of measuring methods: the photogrammetric method, which employs a pair of images, the method of light profiles, which are applied by the laser light and recorded by means of a high-speed digital camera, and the method based on laser radar or laser scanner (lidar) measurements. Those most advanced systems combine the above-referenced measurement methods. The paper demonstrates flaws and advantages of particular systems and provides a technological summary of measuring equipment utilized in them. It results from literature queries performed that presently, in the case ofsystems dedicated to railway clearance diagnostics, these are solutions based on laser scanners, which dominate most often, and which acquire data in the form of crosswise profiles that are recorded perpendicularly to the direction of travel, supported possibly by vision systems. On the other hand, in the case of universal mobile systems, one can notice a distinct domination of joint configurations of laser scanners and digital cameras, supported by INS/GNNS recording. In those systems the measurement of structures is referred to the global system of co-ordinates, and later, upon the detection of rail heads, a transformation to the rail axis arrangement takes place. The preliminary analysis leads to a conclusion that the accuracy of rail clearance measurement is higher in the case of specialised systems as compared to universal ones.
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