# GNSS-Assisted Low-Cost Vision-Based Observation System for Deformation Monitoring
###### Abstract  
This paper considers an approach to solve the structure monitoring problem using an integrated GNSS system and non-metric cameras with QR-coded targets. The system is defined as a GNSS-assisted low-cost vision-based observation system, and its primary application is for monitoring various engineering structures, including high-rise buildings. The proposed workflow makes it possible to determine the change in the structure geometric parameters under the impact of external factors or loads and in what follows to predict the displacements at a given observation epoch. The approach is based on the principle of relative measurements, implemented to find the displacements between pairs of images from non-metric cameras organized in a system of interconnected chains. It is proposed to determine the displacement between the images for different epochs using the phase correlation algorithm, which provides a high-speed solution and reliable results. An experimental test bench was prepared, and a series of measurements were performed to simulate the operation of one vision-based observation system chain. A program for processing the sequence of images in the MatLab programming environment using the phase correlation algorithm was implemented. An analysis of the results of the experiment was carried out. The analysis results allowed us to conclude that the suggested approach can be successfully implemented in compliance with the requirements for monitoring accuracy. The simulation of the vision-based observation system operation with accuracy estimation was performed. The simulation results proved the high efficiency of the suggested system. GNSS; vision-based observation system; structural health monitoring; digital camera; monitoring accuracy; horizontal displacement; deformation monitoring QR target; phase correlation +
Footnote †: journal: Applied Geodesy, Kyiv National University of Construction and Architecture, 00307 Kyiv, Ukraine 2023  
Footnote †: journal: Applied Geodesy, Kyiv National University of Construction and Architecture, 000307 Kyiv, Ukraine 2023  
Footnote †: journal: Applied Geodesy, Kyiv National University of Construction and Architecture, 00307 Kyiv, Ukraine 2023
change their values daily and seasonally [1] and can cause spatial displacements at the tens of centimeters level. The considered geometric deformation parameters that need to be determined during deformation monitoring of the high-rise building are given in Figure 1.  
Evidently, the deformation parameters presented above are subject to monitoring by different geospatial methods and technologies as long as the parameters are functions of linear and angular displacements. Such monitoring is carried out using various methods, geodetics particularly. Today, the global navigation satellite systems (GNSS) are the most widespread element of any monitoring system. GNSS provides reliable and high-frequency information about the monitoring target coordinates' changes. However, due to the impossibility of measuring coordinates along the structure axis from the ground to the top, GNSS data reveals only the total displacement \(\Delta\) of the structure. This displacement may portray the structure's top displacement without reference to the ground floor. Thus, the reason for this displacement is unknown and maybe the simple spatial displacement, displacement and bending, or displacement and roll combinations (see Figure 2). It has become clear that GNSS observations alone cannot accurately depict the deformation process. That is why GNSS may primarily be used as a complementary data source and to help detect the structure's vertical displacement, but additional measurements along  
Figure 1: Monitoring parameters: (**a**) vertical displacements; (**b**) roll; (**c**) bending; (**d**) torsion. Figure 2: The structure displacement caused by either roll or bending in combination with spatial displacement. the structure are needed to figure out the reasons for the structure displacement and to obtain an accurate picture of the deformation process.