Accuracy assessment of levlling staffs marking using digital photocameras

Abstract

The article analyses the determination of accuracy of code levelling staff edges by using their digital photos. The accuracy of the position of graduated lines of levelling staffs is established by comparing reference and test digital photos of levelling staff stored in digital photo camera or in a computer memory. In this case, the position of lines of a calibrated levelling staff is compared to the position of lines of a photogrametric image of a reference levelling staff. Firstly, the digital camera calibration is performed. The aim of the research is to perform the analysis of accuracy of levelling staffs marking's edges by applying lenses of different focal length and to determine which of them provide the most accurate results of calibration. Digital photo camera Canon-EOS-7D, with which digital pictures of levelling staffs scales marking were taken, was chosen for the research and calibrated. The pictures of levelling staffs scales marking were taken with different camera lenses (20, 50 mm) and with different camera modes (auto, macro). Having analysed the obtained results, it was assumed that the focal length of lenses of a photo camera and partially the choice of a camera mode have an influence on final results of calibration. The most accurate results were obtained by taking pictures and calibrating the levelling staffs scales with a 50 mm fixed-focus camera lens.