Transmission line sag measurement based on single aerial image

The sag of power transmission line is of great significance to the safe operation of the whole transmission systems, and is also an important indicator of the line design. A new method to measure the sag of the transmission line was presented in this paper, which was based on the laser ranging and the image processing technology. Firstly, the contrast enhancement and threshold segmentation were used to obtain the binary image with clear contour. Secondly, the connection points between the line and the tower were selected as the interested points, and the improved Harris detection algorithm was used to extract the corner points as well as measure their pixel coordinates. Then the contour fitting of the transmission line was carried out by using the random circle, the hyperbola, and the parabola fitting algorithm respectively. The root mean square error was used to judge the fitting effect, and then the best fitting equation was obtained. Finally, with the Global Positioning System technology to test and verify, the conversion ratio of the image distance and the actual spatial distance was obtained by using the laser ranging technology, and the actual sag of the transmission line was calculated. Compared with the actual measurement results, the measurement error of the new method can be as low as 0.38%, which was within the error tolerance range. This method is simple in operation, low in shooting requirement and fast in coordinate conversion. It can accurately measure the sag of the transmission line, and is suitable for processing complex background environment.