The application of optoelectronic technique of transferring heights from the recessed benchmarks in networks in the examination of rock mass deformation

Abstract

The article presents a new method for transferring height from benchmarks on which the levelling staff cannot be set. The aim of transferring height is tie in measurements to the network. Reference points and control points in geodetic networks used for monitoring deformation of various objects are permanently affixed to various objects such as building walls or the ground. Changes that affect both the technical infrastructure and geological objects cause that some of these benchmarks are permanently destroyed or cannot be accessed to level them. The first of the proposed methods is based on mono-photogrammetry and uses the Direct Linear Transformation (DLT) method. The experimental measuring set proposed to transfer height: camera (CCD / CMOS), a typical levelling staff with box level and the a designed signaling device. The signal device is mounted on the benchmark, and in its vicinity, the levelling staff is set vertically on the levelling plate. A single photo of the signal and the levelling staff was taken, and next the image was transformed by the DLT method. The height difference between the benchmark and the levelling staff foot was determined on this basis. The second proposed method for transferring height, developed by the authors, relies on the levelled laser beam that is emitted from the benchmark towards the levelling staff. The picture of the staff graduation with the laser light spot taken with a digital camera is then processed using photogrammetry in order to find the value of the reference reading. The experimental works that had been carried out enabled to determine the accuracy of the laser reference and its range. The laboratory works discussed within this article indicate that it is possible to create height references with the accuracy of the hundredth parts of a millimetre and to accomplish the reference range up to a few metres. The presented measuring set features the small size and simple operation. ARTICLE INFO