# Visual-Based Positioning of Aerial Maintenance Platforms on Overhead Transmission Lines
## 1 Introduction  
Inspection of power system assets--including conductors, protection systems, towers, transformers and other devices--plays an important role in addressing the growing need for sustainable energy worldwide. High-voltage overhead transmission lines are essential assets in power systems that require careful and frequent monitoring to reduce probable failures related to environmental, operational, animal or human threats [1; 2] and to ensure their proper operation. However, monitoring process is often neglected or shelved due to more pressing priorities, high deployment costs or industrial policies, which brings hardship to both unprepared businesses and society at large [3; 4]. Within this context, the development of machinery based on autonomous robots, dedicated systems and intelligent machines, helps face the increasingly complex challenges within a rapidly expanding power industry [5], ensuring an efficient, cost-effective and safe maintenance process [6]. Currently, robotics presents itself as an affordable alternative to perform maintenance tasks in power systems, due to its technical characteristics, its outstanding performance to improve several industrial process [7] and its adaptability to different and hostile environments such as: electrical substations [8], high voltage overhead transmission lines [9] or power plants [10]. Several mechanisms have been developed to perform inspection tasks in an energized transmission grid. Among the most noteworthy initiatives are brachatiing robots, unmanned aerial vehicles and ground vehicles [9], each with its own advantages, disadvantages and characteristics, as summarized in Table 1. Unmanned aerial vehicles (UAV) have reached technological summit during the last decade [11], due to their top-quality technical and economic performance. During this period of time, UAVs evolved from a niche market of small scale applications to a common inspection, treatment and surveillance platform of electric equipment mounted on transmission grids. This technology can be used to perform inspection tasks of equipment under hazardous conditions or access restrictions, due to it navigation is only affected by Chilean Flight Regulation-DAN 151, where the guidelines to perform the UAV flight over high voltage overhead transmission lines is summarized. Inspection tasks include methods in which a dataset provided by a huge number of different sensors is interpreted by computer analysis to identify specific conditions or certain types of defects [9]. The variety of sensor needs is illustrated in Figure 1. These sensors can be mounted in aerial platforms in order to increase the flexibility, to reduce the inspection time and to avoid operational risks [12]. The use of UAVs has become increasingly popular for visual industry inspection; the systems are equipped with different cameras, which provide image representations in visual, infrared or ultraviolet spectral bands and each of these bands has advantages for detecting a huge number of damages or defects [9; 13]. Of note among the main applications of visual inspection are to evaluate the condition of structural components such as wires [14], conductors [15], and towers and to detect contamination or physical damages on power insulators [16]. In addition, visual inspection work is highly used to detect encroachment on the ground or near the tower structure. In off-line applications, the UAV can store several images of the transmission grid, which are analyzed to detect patterns that would indicate fatigue, cracks [17], rust, corrosion [18] or other damages. In addition, the surveillance of transmission lines against terrorist attacks can be developed by UAVs [19]. The thermal analysis provides relevant information about the status of different mechanisms mounted on a transmission grid [20]. Currently, this process is carried out with a wide range of real-time monitoring devices that determine the dynamic thermal rating of a transmission grid [20; 21; 22] and are mounted on the line.