Precise Measurement of Retro-Reflective Targets Using Improved Ellipse Fitting Technique

Close-range Photogrammetry is widely used in industrial applications for measuring size, shape and deformation of objects. In industrial photogrammetry, circular targets are often utilized to increase the automation as well as the accuracy of measuring process. Edge based and area based methods can be applied for locating the centroid of these targets. In this paper, an improved ellipse fitting technique is proposed to increase the accuracy and precision of determining center location of the targets. Various tests including size, orientation and elongation under varying conditions are performed on both simulated and real targets to evaluate the reliability of the proposed method. Obtained results proved the higher accuracy of the proposed method in comparison with the other traditional methods.