Measurement method of shipborne rudder angle dial indication based on pointer gray distribution features

Abstract To address the weak environmental adaptability and low computational efficiency of existing image recognition methods for shipborne rudder angle dial indications, a measurement method based on pointer gray distribution features is proposed. By analyzing the significant gray difference between the pointer and the background area of the rudder angle dial, a detection framework incorporating scan boundary setting, radius optimization, and gray intensity curve analysis is constructed. A pointer calculation model is established based on the relationship between the extremum points of the average gray intensity distribution curve of scanning lines and the rudder angle. Furthermore, the influence of scanning center position deviation on measurement accuracy is quantitatively analyzed. The robustness of the method is verified through a multi-modal interference test set including strong light, weak light, reflections, and fluorescence. This technology has been applied in the ship trials of the Yangtze-to-Huaihe Water Diversion Project’s ultra-long channel. Test data show that the full-scale measurement error does not exceed 0.8°, with a processing efficiency exceeding 30 Hz. Compared with traditional methods, this approach achieves simultaneous optimization in environmental adaptability, computational efficiency, and real-time performance, meeting the stringent requirements of ship trials for strong anti-interference capability, high precision, and real-time operation.