A novel cross-circular coded target for photogrammetry

Abstract

This paper presents a new type of coded target having cross and circular points and its identification, positioning and decoding method are discussed. The cross symbol is used to locate the target quickly and construct affine transformation. The arrangements of the circular points represent the coded information. The design scheme can produce a rich number of coded targets. Firstly, shape factors and modular match are employed to segment and discriminate the target features. Then, the cross skeleton is extracted using K3M algorithm (K Saeed, M Dzki, M Rybnik, M Adamski). Based on the interposition on the normal direction of the cross skeleton, a sub-pixel algorithm to minimize continuous curvature change is proposed to obtain the image coordinates of the cross. At last, a decoding method based on affine transformation is proposed. The affine transformation matrix is solved according to the relationship between the cross ending points on the design module and on its image. The images of several coded targets shot from different angles and distances are analyzed and decoded, and a dynamic experiment of the wind turbine blade have carried out. Experimental results show that the coded target designed is quite applicable and the decoding algorithm is fast and stable.