# GNSS-Assisted Low-Cost Vision-Based Observation System for Deformation Monitoring
###### Abstract
The given list [71; 72; 73; 74; 75; 76; 77; 78; 79] is just about geometric parameters deformation monitoring. Thanks to the development of digital technologies and computer science, it is possible to use different small sensors and combine them into one system that may operate automatically. However, modern SHM systems may also include satellite-based interferometry [80; 81; 82; 83], UAV technologies [84], and terrestrial and/or aerial laser scanners [6]. Moreover, the SHM system is also a part of another more complex system named the building information model (BIM) [85; 86; 87; 88]. BIM comprises all possible building life-cycle stages and consequently the monitoring steps. The paper [88] outlines the liaison between monitoring problems and BIM. Thus, the creation and operation of any monitoring system should be considered an inseparable part of the building life cycle and must be embedded into BIM. This premise imposes the conditions of easy installation, repair, operation, relocation, and renovation of the monitoring system. Such complicated requirements can be fulfilled for a system that consists of low-cost sensors. On the other hand, the system design must be as simple as possible and reliable. Based on the given analysis, it was suggested to deploy low-cost digital cameras operating in an automated mode and organized in a system of chains connected with each other. GNSS is supposed to be used as a supplementary data source that provides external reference and control. The system is assumed to be installed inside the building and integrated into BIM. Such a system is easy to install and use, has high reliability due to the vast redundancy of measurements, and does not need professional users. This study aimed to introduce the GNSS-assisted low-cost vision-based observation system (VOS) concept and demonstrate the system's preliminary analysis results. This system includes the ideas and approaches from close-range photogrammetry to calibrate and orient images; computer vision to process digital images; geodesy to assign coordinate systems and external control (including the possible application of total stations and GNSS); and adjustment calculus to process and analyze the measurement results. The suggested approach provides complex information about a structure deformation and reduces error accumulation and the effect of external errors, increasing the resulting accuracy in determining the displacement values. The study of [89; 90; 91] has shown that to carry out complex deformation research, it is recommended to locate the system chains along the principal axes of the structure. A couple of papers demonstrate a very tentative approach with a similar idea. In [92], the approach of relative displacement measurements from the inside using an in-room camera is presented. The paper considers just a particular case of observations using one camera from one point. A more detailed review is outlined in [93], with good analysis and ideas a bit similar to our study. However, the work did not consider the case of combining a set of cameras into a network. The significant contribution of this paper is the analysis of the measuring accuracy ensured by the computer vision monitoring systems and target tracking algorithm examination. The study [94] demonstrates a concept that is close to the VOS idea but is mostly about camera calibration and does not consider cameras organized into a system without external control. Therefore, the existing approaches and methods have some similarities to the VOS concept that will be presented and studied in what follows. The following stages have to be examined to achieve the primary goal of the study:  
1. General idea and concept description. 2. Design of the VOS. At this stage, the distance effect between the VOS elements is considered based on the camera's technical capabilities and the geometric parameters of the test structure. 3. Determination of displacements between VOS elements for a single chain. In-field simulation of the displacement measurements for a single chain.