Abstract: In order to achieve the automatic obstacle avoidance of unmanned aerial vehicle (UAV) during substation inspection, this paper proposes a UAV autonomous positioning method by using encoded sign as control point. First, the design and decoding of encoded sign are discussed. Second, the encoded signs in the image are detected by using the SVM+HOG algorithm, and the tracking algorithm is used to track the encoded sign efficiency. At last, according to the location of encoded signs on the pylon and its corresponding coordinates on the image, the location of UAV can be calculated by using the projective relation between the object points and their corresponding image points. Experiments show that the set of SVM+HOG can detect the encode signs in the image at a recall rate of 99%, and the decoding algorithm remains strong robustness in signs blur, deformation and other extreme conditions, with decoding error rate of only 0.05%. The error of UAV positioning is not more than ±0.03 m, and the algorithm runs at a speed of 10 frames per second, fast enough for practical substation inspections.

Key words: support vector machine (SVM), encode sign, unmanned aerial vehicle (UAV), histogram of oriented gradient (HOG), substation inspection