The alpine terrain with its exposed georelief and climatic conditions supports a wide range of natural processes with various morphodynamic phenomenons. The National Park of High Tatras is probably the most visited park in Slovakia and the instability of talus cones during times of of torrential rains thus may present a significant danger to the tourists in their vicinity. In this paper we present a procedure for documenting and monitoring the talus cone stability, which is a typical geological phenomenon in alpine areas, using the SfM (Structure from Motion) method based on UAS imaging. A significant problem of documentation in the alpine environment is posed by the character of the terrain, which is inclined with a slope usually between 20° and 60°, often very rugged, consisting essentially of larger or smaller boulders ranging in sizes from 10 cm to 1 m (often with the occurrence of isolated stone blocks of several meters). In our study, we have shown that in difficult mountain conditions, UAS photogrammetry is capable of providing models of comparable quality with those acquired by TLS for monitoring movement of the talus cones. Mean absolute deviation of 0.028 m and a standard deviation at an absolute distance of 0.029 m. A mean difference of 0.008 m is practically negligible in the altitude component, and the standard deviation is 0.032 m we can conclude that with the exception of vegetation-covered areas, the terrain model obtained from low-cost UAS photogrammetry achieves qualitative (precision) parameters comparable to those obtained by terrestrial laser scanning and is thus suitable as a basis for systematic monitoring that will form a basis for identification of surface changes at the centimeter level.
All surveying instruments and their measurements suffer from some errors. To refine the measurement results, it is necessary to use procedures restricting influence of the instrument errors on the measured values or to implement numerical corrections. In precise engineering surveying industrial applications the accuracy of the distances usually realized on relatively short distance is a key parameter limiting the resulting accuracy of the determined values (coordinates, etc.).
To determine the size of systematic and random errors of the measured distances were made test with the idea of the suppression of the random error by the averaging of the repeating measurement, and reducing systematic errors influence of by identifying their absolute size on the absolute baseline realized in geodetic laboratory at the Faculty of Civil Engineering CTU in Prague. The 16 concrete pillars with forced centerings were set up and the absolute distances between the points were determined with a standard deviation of 0.02 millimetre using a Leica Absolute Tracker AT401.
For any distance measured by the calibrated instruments (up to the length of the testing baseline, i.e. 38.6 m) can now be determined the size of error correction of the distance meter in two ways: Firstly by the interpolation on the raw data, or secondly using correction function derived by previous FFT transformation usage.
The quality of this calibration and correction procedure was tested on three instruments (Trimble S6 HP, Topcon GPT-7501, Trimble M3) experimentally using Leica Absolute Tracker AT401.
By the correction procedure was the standard deviation of the measured distances reduced significantly to less than 0.6 mm. In case of Topcon GPT-7501 is the nominal standard deviation 2 mm, achieved (without corrections) 2.8 mm and after corrections 0.55 mm; in case of Trimble M3 is nominal standard deviation 3 mm, achieved (without corrections) 1.1 mm and after corrections 0.58 mm; and finally in case of Trimble S6 is nominal standard deviation 1 mm, achieved (without corrections) 1.2 mm and after corrections 0.51 mm.
Proposed procedure of the calibration and correction is in our opinion very suitable for increasing of the accuracy of the electronic distance measurement and allows the use of the common surveying instrument to achieve uncommonly high precision.
The prestressed thin-walled concrete elements enable the bridge a relatively large span. These structures are advantageous in economic and environmental way due to their thickness and lower consumption of materials. The bending moments can be effectively influenced by using the pre-stress. The experiment was done to monitor deformation of the under load. During the experiment the discrete points were monitored. To determine a large number of points, the intersection photogrammetry combined with precise micro-network were chosen. Keywords:
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