## 5 Method Modifications
### Calibration Refinement during the Robot's Operation  
During the robot's operation, the calibration may become irrelevant. The camera calibration can only be affected by a change in camera characteristics (camera replacement) or a change in focal length (which is fixed for these robots), so recalibration is most often required only when changing the camera, which does not happen often. The situation with recalibration of motors is somewhat different. It can be influenced by various factors: a change in the wheel diameter due to wear of the wheel coating, a slight change in the characteristics of motors due to the wear of the gearbox plastic, and a change in the robot's weight distribution, e.g., laying the cables on the other side of the case after charging the robot, and so a slight calibration mismatch can occur. However, all these factors have a rather small impact, and the robot will still have a satisfactory calibration. There is no need to re-perform the calibration process, just a little refinement of the current one seems to be enough. It was decided to support this functionality. To do this, a section of the road along which the robots will be guaranteed to pass regularly, was selected. Depending on the algorithms of the robot and the configuration of the city, these can be different sections; in this case the section along which the robot leaves the recharging zone was chosen. Further, markers were placed in this lane according to the rules described earlier: the distance between the markers is 15 cm; the size of the marker is 6.5 cm, as presented in Figure 6. The markers are located in the center of the lane. The distance between the markers may be not completely accurate, but they should be oriented in the same direction and co-directed with the movement in the lane on which they are placed. An important condition is that the markers must be placed on a straight road section and have at least one field tile with a straight road section at the beginning and at the end of the section, the number of markers is known as well. The first marker in the direction of travel must have a predefined ID. It can be anything, the only limitation is that it must be unique for a current robot environment. Further, the following changes were made to the algorithm for the standard control of the robot: when the robot recognizes the first marker with a predetermined ID while driving right in the lane, it corrects its orientation relative to this marker and continues to move strictly straight ahead. Further, the algorithm is similar to the one described earlier--the robot recognizing the next marker can refine its wheel calibration coefficient, apply it, and change the orientation coaxially with the next marker. The number of iterations depends on the number of markers located on the calibration road segment. This approach serves to perform calibration without affecting the main task of the robot on a given segment--moving in the lane. This approach can be followed an arbitrary number of times, and since the algorithm applies new values of the calibration coefficient only when the new value is constant and significantly different from the current one, it ensures that a random error will not negatively affect the currently used coefficient.  
Figure 6: Markers’ locations for auto-calibration in lane.