Robust virtual encoder: Using ultrasound data for compensation of depth variations in camera-based odometry

Ultrasonic inspection with mechanical movement requires accurate odometry to properly localize flaws. A camera-based odometry system (termed ‘virtual encoder’) was recently proposed as a versatile solution to substitute mechanical encoders for 2-D and 3-D displacements. However, this solution assumes a fixed distance between the camera and the inspected specimen, making it less accurate when this distance varies. In this paper, we address this problem by leveraging the available ultrasonic data in the odometry system. Our method utilizes the ultrasonic RF signal from an immersion test to estimate the distance, which is then used in a displacement compensation method. We compare the fixed-distance approach and the proposed method over a 20 mm to 40 mm distance range, and our model achieves an accuracy improvement of at least 10%.

Proceedings of the 14th European Conference on Non-Destructive Testing (ECNDT 2026)