The paper contains a survey of mobile scanning systems for measuring the railway clearance gauge. The research was completed as part of the project carried out for the PKP (PKP Polish Railway Lines S.A., Warsaw, Poland) in 2011–2013. The authors conducted experiments, including a search for the latest solutions relating to mobile measurement systems that meet the basic requirement. At the very least, these solutions needed to be accurate and have the ability for quick retrieval of data. In the paper, specifications and the characteristics of the component devices of the scanning systems are described. Based on experiments, the authors did some examination of the selected mobile systems to be applied for measuring the clearance gauge. The Riegl (VMX-250) and Z+F (Zoller + Fröhlich) Solution were tested. Additional test measurements were carried out within a 30-kilometer section of the Warsaw-Kraków route. These measurements were designed so as to provide various elements of the railway infrastructure, the track geometry and the installed geodetic control network. This ultimately made it possible to reduce the time for the preparation of geodetic reference measurements for the testing of the accuracy of the selected systems. Reference measurements included the use of the polar method to select profiles perpendicular to the axis of the track. In addition, the coordinates selected were well defined as measuring points of the objects of the infrastructure of the clearance gauge. All of the tested systems meet the accuracy requirements initially established (within the range of 2 cm as required by the PKP). The tested systems have shown their advantages and disadvantages.

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. The paper demonstrates flaws and advantages of particular systems and provides a technological summary of measuring equipment utilized in them. In those systems the measurement of structures is referred to the global system of coordinates, and later, following 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 specialized systems as compared to universal ones. On the basis of experience drawn from literature and earlier tests, a decision has been made to proceed with the construction of a rail clearance measurement system in Poland, at the University of Science and Technology in Cracow. This paper presents a research on the prototype of the rail clearance measurement system constructed at the University. The heart of the system involves laser scanners installed on a flatcar and digital cameras. The base of the system includes scanners, which capture data in a continuous way, and photogrammetric cameras, which yield digital images. The cloud of points obtained from a laser scanning is colorized, which causes that such information can replace a classical texture model.