Contactless measurement of rectilinearity of an elongated object based on the example a crane rail

The common aim of engineering surveys is to determine deviations from rectilinearity for elongated objects. We have developed a number of methods for measuring points that represent an elongated object. These are the constant straight (optical, laser, mechanical-string) method, the trigonometric method, geometric levelling method, photogrammetric methods and terrestrial laser scanning. When taking these measurements, it is crucial to have a direct access to the survey points of the measured object. Factors impeding the measurements include: adverse lighting conditions, vibration, dust, refractory effects, lack of direct access to the survey points, etc. The authors have developed a measurement methodology and designed a measuring set for taking measurements that enable to determine the location of survey points on an elongated object. The measurement is based on the constant straight method and the measuring set consists of the horizontal levelling staff and two laser pointers. The measuring set relies on the angular intersection (fixed angle) method. Intersection occurs when two laser beams meet. To determine the location of the survey point indicated by the mentioned laser beams, we used levelling staff readings taken with the surveying instrument that establishes the reference constant straight. Experimental studies carried out in the laboratory and in the field helped to determine the accuracy of measurements taken with the designed measuring set (the accuracy was below ± 1 mm) and revealed that this accuracy is comparable to accuracies achieved with famous classical measurement methods.