Problem statement: Smart electromechanical systems (SEMS) can be used to control the elements of the radio telescope surface. For this purpose, we can use robotic platforms with a surveillance system. Elements of the surface have mechanisms for adjusting the position in space. The platform, in accordance with the reflected marks, calculates the relative position of the surfaces and commands to the adjustment mechanisms to correct the position in space. When the displacements are extremely small in the observation plane, the images of the mark practically merge and as a result, this error can't be corrected. Purpose of research: development of an algorithm capable of measuring the displacement error for small displacements. Results: algorithms of image selection in the analysis plane are considered. A mathematical model of the problem of overlapping marks developed. An algorithm for measuring the coordinates of overlapping marks was developed and tested. The algorithm is tested using an autocollimation scheme as a platform surveillance system. Practical significance: The developed algorithm allows reducing the zone of inoperability of the device, to increase the accuracy of the adjustment of surfaces. The algorithm opens up new opportunities for SEMS and another measurement system.