UAV Low Altitude Photogrammetry for Power Line Inspection

Abstract

When the distance between an obstacle and a power line is less than the discharge distance, a discharge arc can be generated, resulting in the interruption of power supplies. Therefore, regular safety inspections are necessary to ensure the safe operation of power grids. Tall vegetation and buildings are the key factors threatening the safe operation of extra high voltage transmission lines within a power line corridor. Manual or laser intensity direction and ranging (LiDAR) based inspections are time consuming and expensive. To make safety inspections more efficient and flexible, a low-altitude unmanned aerial vehicle (UAV) remote-sensing platform, equipped with an optical digital camera, was used to inspect power line corridors. We propose a semi-patch matching algorithm based on epipolar constraints, using both the correlation coefficient (CC) and the shape of its curve to extract three dimensional (3D) point clouds for a power line corridor. We use a stereo image pair from inter-strip to improve power line measurement accuracy by transforming the power line direction to an approximately perpendicular to epipolar line. The distance between the power lines and the 3D point cloud is taken as a criterion for locating obstacles within the power line corridor automatically. Experimental results show that our proposed method is a reliable, cost effective, and applicable way for practical power line inspection and can locate obstacles within the power line corridor with accuracy better than ±0.5 m.

Automatic Power Line Inspection Using UAV Images

“…All of the objects in the power line corridor with a distance to the power line that is less than the safety distance are defined as obstacles [21]. As shown in Figure 1, to detect obstacles within the power line corridor, we first use UAV images and ground control points (GCPs) to obtain the exterior orientation of images (EOIs) via block bundle adjustment (BBA).…”

“…Each tower has three separated power lines, and thus, the total length of the power lines is 11.7 km (11.7km = 3.9km × 3). The same fixed-wing UAV found in reference [21], with a Nikon D810 camera (focal length: 51.42 mm, complementary metal oxide semiconductor (CMOS) sensor, 35.9 mm × 24.0 mm, 7360 × 4912 pixels, pixel size: 4.88 µm) is adopted for the photography of the power line corridor. The camera interior parameters were calibrated before commencing aerial photography.…”

“…For an efficient matching algorithm, we applied the SPMEC, which was proposed in reference [21]. The principle of the SPMEC is as follows: first, an initial parallax mesh is constructed using tie points; second, the match window slides along the epipolar line within a certain search window guided by the initial parallax; finally, a tentative match is determined by applying a similarity measure for the shape of the correlation coefficient curve within a certain search window, and the 3D reconstruction process is completed.…”

“…In this paper, based on the work discussed in the literature [21], we focus on the automatic measurement of power line 3D coordinates using UAV images to improve the automation level of power line inspections. Details of the proposed power line automatic measurement method based on epipolar constraints (PLAMEC) are described in Section 2.1.…”

“…A 3D reconstruction of the power lines and the ground can be performed using photogrammetric methods, and the obstacles can be automatically identified and located by calculating the spatial distance between the power line and the ground. In reference [21], we proposed a dense matching algorithm for the 3D reconstruction of the ground in power line corridors known as SPMEC, which has accomplished the automatic 3D reconstruction of objects such as the crowns of trees and roofs within a power line corridor. For a 3D reconstruction of power lines, we adopted the traditional manual stereo measurement method, which restricts the level of automation of inspection by using UAV images and which needs further improvement.…”