The Swarm Intelligence Freeway–Urban Trajectories (SWIFTraj) Dataset–Part II: A Graph-Based Approach for Trajectory Connection

In Part I of this companion paper series, we introduced SWIFTraj, an open-source vehicle trajectory dataset collected by a UAV swarm. It provides long-distance continuous trajectories by connecting vehicle trajectories across consecutive UAV videos, with the longest trajectory exceeding 4.5 km, and covers an integrated network of freeways and connected urban roads. However, trajectory connection in UAV swarms is challenging because of video time-offset errors and irregular UAV layouts. To address these issues, this paper proposes a graph-based trajectory connection method. An undirected graph is used to represent flexible UAV layouts, an automatic time-alignment method is developed by minimizing trajectory matching costs, and cross-video vehicle association is performed using a Hungarian-algorithm-based matching table. Experiments on real-world and simulated data show that the proposed method achieves time alignment errors within three frames, about 0.1 s, and consistently high vehicle-matching F1-scores.