The Measurement Of Transmission Line Length And Sag Based On Bidirectional Close-range Photogrammetry Mode

The transmission line is an important basis equipment of the electric powertransmission in the electric power system, it is an important premise ensuringthe safe operation of the circuit that the sag size was guaranteed within theprescribed scope. As the transmission line was in the bare state for a long time, itsubjected to various external violation (pollution, strong wind, rainstorm, hail,Blizzard and bird etc.),and these reasons caused changes on transmission linesag. Therefore, the transmission line need regular inspection to ensure that itssag in the specified range.This paper proposed the bidirectional close range photogrammetry mode toachieve the measurement of transmission line length and sag due to the lowefficiency of the traditional method and the high cost of aerial photogrammetry.This method acquired the transmission line images from the two oppositedirection, no matter which direction the camera axis was vertical to thetransmission line, and regarded the separation bar of the transmission line imageas the characteristic, and extracted the center point of the characteristic throughthe feature extraction and homonymy points matching between images andtaken it as the point to be measured, at the same time, and measured the3Dcoordinate of points laid on the transmission line tower using total station andtaken them as the control point, obtained the exterior orientation elements,distortion coefficient and the3D coordinates of the these measuring point of the image with self-calibration bundle adjustment, and curved these measuring pointand got the transmission line length and sag.This paper first established the coordinate calculation model and theaccuracy model of the measuring points through the bidirectional close rangephotogrammetry model, the precision of the bidirectional photography is aboveto the one-way photography which is verified according to the calculation model.It established the self calibration bundle adjustment to slove the inner andexterior orientation elements, the distortion coefficient and the measuring pointcoordinate of the transmission line image.At the same time, this paper proposed a matching algorithm combined theHarris corner extraction with SIFT feature matching for their complementarycharacteristics when involved the separation bar features extraction andhomonymy points matching between images, which considering the matchingstrategy of from coarse to fine and Pyramid hierachical and the matchingconstraints of the bidirectional consistency.Finally, the two-dimensional curve was fitting with the3D coordinate dataof the center points of transmission line spacing bar by using the least square.With the curve the coordinates of the hanging points and the lowest point wascalculated and realized the measurement of the transmission line length and sag.The experimental simulation was done for the transmission line the model,and the results show that the measurement of the arc length and sag oftransmission line can be realized by the bidirectional close-rangephotogrammetry.