Hit-Guided Monocular 3D Shuttlecock Trajectory Reconstruction via 3D-Oriented Robust 2D Tracking and Multi-Constraint Modeling

Recovering the three-dimensional trajectory of a shuttlecock from fixed monocular match videos is important for landing-point judgment, net-clearance analysis, flight-curve modeling, and stroke-quality assessment. Existing monocular badminton 3D recovery pipelines usually integrate court geometry, player pose, 2D shuttle trajectories, hit events, and physical constraints, demonstrating the feasibility of this task; however, in real matches, the shuttlecock is small and fast, and long 2D gaps, local large deviations, and hit-event misjudgments may still be amplified during 3D modeling, while frame-wise 3D ground truth is also scarce. To address these problems, this paper proposes a hitguided monocular 3D shuttlecock trajectory reconstruction method. The method first builds a 3Doriented robust 2D trajectory processing framework, improving the continuity and reliability of 2D inputs through multi-source candidate evidence, conservative selection, and candidate-level calibration; it then uses hit-to-hit flight segments as the basic unit and recovers segment-wise continuous 3D shuttlecock flight curves by combining court-camera geometry, 2D reprojection, pose semantics, and gravity-drag physical constraints. The evaluation is organized according to the task pipeline: 2D trajectory annotations are used to assess the quality of the preceding observation stage, ShuttleSet/ShuttleSet22 event annotations are used for posterior event-level consistency analysis, and curated high-confidence stereo3D clips are used for external 3D spatial reference validation. The results show that the proposed method increases F1@15px from 87.04% to 89.56% and reduces Danger@15 from 21.70% to 17.49% at the 2D observation level; under the given-hit protocol, the mean 3D error on stereo3D reference segments decreases from 2.680 m to 2.153 m, and the P90 3D error decreases from 8.291 m to 4.369 m. These results indicate that the proposed method can recover more continuous, stable, and physically interpretable 3D shuttlecock trajectories from real monocular match videos, providing a reliable spatial motion basis for stroke-quality assessment, tactical review, and sports video analysis.