Abstract
Regular inspection of transmission lines is an essential work, which has been implemented by either labor intensive or very expensive approaches. 3D reconstruction could be an alternative solution to satisfy the need for accurate and low cost inspection. This paper exploits the use of an unmanned aerial vehicle (UAV) for outdoor data acquisition and conducts accuracy assessment tests to explore potential usage for offsite inspection of transmission lines. Firstly, an oblique photogrammetric system, integrating with a cheap double-camera imaging system, an onboard dual-frequency GNSS (Global Navigation Satellite System) receiver and a ground master GNSS station in fixed position, is designed to acquire images with ground resolutions better than 3 cm. Secondly, an image orientation method, considering oblique imaging geometry of the dual-camera system, is applied to detect enough tie-points to construct stable image connection in both along-track and across-track directions. To achieve the best geo-referencing accuracy and evaluate model measurement precision, signalized ground control points (GCPs) and model key points have been surveyed. Finally, accuracy assessment tests, including absolute orientation precision and relative model precision, have been conducted with different GCP configurations. Experiments show that images captured by the designed photogrammetric system contain enough information of power pylons from different viewpoints. Quantitative assessment demonstrates that, with fewer GCPs for image orientation, the absolute and relative accuracies of image orientation and model measurement are better than 0.3 and 0.2 m, respectively. For regular inspection of transmission lines, the proposed solution can to some extent be an alternative method with competitive accuracy, lower operational complexity and considerable gains in economic cost.
Highlights
Modern society is becoming increasingly more dependent on reliable supply and distribution of electric power
The dual-camera system makes it possible to construct stable image connection network, especially for image pairs captured in opposite directions
This research introduces a unmanned aerial vehicle (UAV)-based oblique photogrammetric system for image data acquisition and conducts necessary accuracy assessment experiments for image orientation and model measurement to explore the potential usage for offsite inspection of transmission line
Summary
Modern society is becoming increasingly more dependent on reliable supply and distribution of electric power. In order to minimize outage of power system, transmission lines are regularly inspected by electricity companies to detect potential risks, such as vegetation encroachment, corrosion of conductor, and pylon overload [1,2]. The most common approaches for power line inspection are foot patrol and helicopter-assisted inspection. There are usually two inspectors who walk towards each. For helicopter-assisted inspection, the helicopter flies over power lines while inspectors use some instruments, such as binoculars or video cameras, to record images for onboard or laboratory check. Because power lines are usually located in mountainous areas and visual inspection is a subjective matter, both methods are either time consuming or very expensive as well as prone to mistake-making [1]. Because of expansion of power grid and enhancement of voltage level, these traditional manual operation modes less and less satisfy the demand of fast, safe and low cost inspection
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