Measurement of Transmission Line Sag Based on Video Image

The sag and the distance to the ground of transmission lines are the main indicators of the line design and operation, and the accurate measurement of the two indicators is extremely important for the safe operation of line. Combining image processing and photogrammetry technology, a new transmission line sag measurement method is proposed in this research. The unmanned aerial vehicle (UAV)-based data acquisition system was used to take multiple on-site images from the same transmission line at different shooting positions and angles. The image segmentation algorithm combining smoothing filtering, edge detection and boundary tracking was used to identify the sag feature points in the images. The stereo image pair forward intersection algorithm was used to derive the actual coordinate value of the corresponding sag point. Then, the accurate measurement of the transmission line sag and the distance to the ground was achieved. Compared with the actual measurement results of the on-site laser rangefinder, the average error of the new measurement method was less than 1.3%, and the maximum error was less than 2.8%, indicating that the proposed method was correct and effective and could meet the needs of practical applications.