Adaptive‑size fiducial‑marker detection with dual‑stage Kalman filtering for precision UAV landing

Precision UAV landing systems face significant challenges with traditional fixed-marker approaches, particularly under varying environmental conditions and integration scenarios. This paper presents a novel approach combining dynamically-sized fiducial markers with dual-stage Kalman filtering to address these limitations. The methodology utilizes a 13.3-inch e-ink display showing ArUco markers that dynamically scale from 16.7 cm to 2.8 cm during descent, actively reducing marker size while accounting for e-ink display refresh constraints through predictive state estimation. A vision system processes frames at 30Hz through an optimized detection pipeline, while the dual-stage Kalman filter handles both vehicle state estimation and parameter adaptation, managing display transition dynamics. The system's universal protocol framework enables compatibility with both integrated and unknown UAV platforms through a dual-mode detection approach, combining passive visual detection with active altitude signalling. Experimental validation using a DJI F450 platform with downward-facing camera demonstrates the system achieves mean landing errors of 1.95 cm under wind conditions up to 15 km/h, representing a 59% improvement over fixed-marker approaches. The e-ink display enables reliable marker detection up to 14.2 m altitude under direct sunlight conditions, outperforming LCD displays which become undetectable in bright conditions. Pixel-wise RMSE improved from 150.3 to 140.5 (x-axis) and 170.8 to 151.4 (y-axis) over four sequential landings, demonstrating robust operation across varying integration scenarios.