A photogrammetric solution for measurement of power lines sag via integration of images and accelerometer data of a smartphone

چکیده مقاله

Measuring the sag of electrical power transmission cables is an index for sensing their internal tension and safeties. Accordingly, their measurement is on the agenda of periodic monitoring of power transmission lines. Traditionally, the sags of cables are measured by costly instruments and approaches or anticipated through visual investigations. Some of the approaches are hard to do and also perilous where are used the contact instruments for measurements. Visual investigations are also prone to uncertainty. In this paper, a simple photogrammetric solution is proposed to measure the sags of power cables, which only requires an image taken by a smartphone equipped with an internal accelerometer. In this method, the sag of a cable is estimated by measuring the image positions of the cable supporting points as well as at least two other points lying on it. The used mathematical model is a modified version of the well-known co-linearity condition in which the 3D locus of cables has been modeled with a parabola equation. Accelerometer measurements are used to prevent the ill-posed conditions of unknowns’ estimation and are also contributed to generating the control data for space resections. This method does not require any ground control points to estimate the unknown parameters as well as the sags values, and just a direct distance between the supporting points of cables is its required control information. The proposed solution, while simple, significantly has reduced the risks and costs of measuring the cable sags. On average, the obtained results indicate a relative accuracy of 2.6% in the estimation of the sags of the electrical power transmission cables.