THE METHOD OF MEASURING THE MEMBRANE COVER GEOMETRY USING LASER SCANNING AND SYNCHRONOUS PHOTOGRAMMETRY

The authors present the experience and results of field studies carried out at the technical acceptance of Forest Opera (name in Polish: Opera Lesna) in Sopot (Poland). An unusual design of covering made in the form of "Sheerfill I" technical fabric membrane required spanned in the form of sails, required the use of terrestrial laser scanning. Such approach allowed for the fast and accurate record of the surface of individual panels of roof as a form of point sets with the coordinates of XYZ. At the same time the vibrations occurring on the fabric resulted in the need to verify the measurements using synchronous digital cameras with reference to the methods of close range photogrammetry. Measurements were made in order to realize the technical expertise at the acceptance, after the repairs of the facility. One of the subjects of the study was to determine the condition of the roof membrane effort for six central panels of covering, taking into account the forces that may impact on the membrane e.g. due to snow load. The registration of the membrane shape without load was carried out using laser scanner for all 10 covering panels. During the loading of covering (18 combinations of configurations), the measurement of modified shape of technical fabric panels was performed and verified using geodetic methods (on-line monitoring of the construction and tachometric and photogrammetric measurements). In order to automate the measurement, the authors software was prepared (dedicated to the processing of large sets) and this allowed to accelerate the analysis of geometry for the individual panels with the use of scans obtained from TLS (Terrestrial Laser Scanning). In addition, it allowed to select from a huge number of scan points on roofing panels the optimum amount of numerical data to produce model analyses using the finite element method. The problems presented in this paper indicate the extending the possibility to use the laser scanning also in relation to membrane roofing that subject to vibration. The executed studies shown that the use of TLS and appropriate software dedicated to the elaboration of the harmonically oscillating surfaces allows for the approximation of the changes in geometry at the level which is optimal for the described analyses and during the accepted time.