Abstract
Employing unmanned aerial vehicles to conduct close proximity inspection of transmission tower is becoming increasingly common. This article aims to solve the two key problems of close proximity navigation—localizing tower and simultaneously estimating the unmanned aerial vehicle positions. To this end, we propose a novel monocular vision–based environmental perception approach and implement it in a hierarchical embedded unmanned aerial vehicle system. The proposed framework comprises tower localization and an improved point–line-based simultaneous localization and mapping framework consisting of feature matching, frame tracking, local mapping, loop closure, and nonlinear optimization. To enhance frame association, the prominent line feature of tower is heuristically extracted and matched followed by the intersections of lines are processed as the point feature. Then, the bundle adjustment optimization leverages the intersections of lines and the point-to-line distance to improve the accuracy of unmanned aerial vehicle localization. For tower localization, a transmission tower data set is created and a concise deep learning-based neural network is designed to perform real-time and accurate tower detection. Then, it is in combination with a keyframe-based semi-dense mapping to locate the tower with a clear line-shaped structure in 3-D space. Additionally, two reasonable paths are planned for the refined inspection. In experiments, the whole unmanned aerial vehicle system developed on Robot Operating System framework is evaluated along the paths both in a synthetic scene and in a real-world inspection environment. The final results show that the accuracy of unmanned aerial vehicle localization is improved, and the tower reconstruction is fast and clear. Based on our approach, the safe and autonomous unmanned aerial vehicle close proximity inspection of transmission tower can be realized.
Highlights
The power transmission tower (PTT) provides a crucial foundation for economic development
We take advantages of the intersections to improve the performance of line detection in a heuristic way shown as follows: 1) The segments which should belong to one straight line are merged based on their differences in direction and distance
We evaluated four effective line detection methods which are commonly used in the literatures: Progressive Probabilistic Hough Transformation (PPHT),[61] LSD,[47] EDLine,[62] and fast line detector (FLD).[63]
Summary
The power transmission tower (PTT) provides a crucial foundation for economic development. Passing across various obstacles on the lines has always been a major weakness for RWR.[1,2] LineScout,[9] a successful wire-climbing robot in recent years, was designed with a LineArm to grasp on both sides of the obstacle and flipped its wheel frame to overcome obstacles. It loses efficiency when encountering complicated conductor connection on pylon
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