Abstract. A method for digital processing of the image of sighting target contour in the frequency domain is presented, which makes it possible to significantly improve the accuracy of the optoelectronic device when measuring the angular coordinates of objects. The contour of the sighting target image is represented in the complex plane by constructing its profilogram relative to the base circle. To analyze and calculate the errors in determining the contour, the Fourier image of the expanded profilogram of the target contour is obtained by applying a discrete Fourier transform, which makes it possible to determine the scattering characteristics of the random component of the error in measuring the coordinates of the center of the sighting target contour and to evaluate the errors of its image parameters measurement. The contour parameters of the sighting target are determined using the Spragg formulas by solving the optimization problem of calculating the minimum of a smooth objective function. According to results of target image filtering with the help of an ideal high-pass filter, the absolute error in measuring the sighting target angular coordinates is reduced by more than two times relative to results obtained using the least squares method. The application of methods of digital image processing of the sighting target in the frequency domain enables to bring the measurement error of the angular coordinates of the optoelectronic device within the limits of the permissible average square error of angle measurement for a total station of technical accuracy class.

Keywords: sighting target, optoelectronic device, digital image processing, frequency domain, Fourier transform, additive noise, high-pass filter, profilogram

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