DHM-RRT*: Dynamic Hybrid Multi-Strategy RRT* for 3D UAV Path Planning

Abstract

In complex three-dimensional airspace, UAV trajectory planning is subject to stringent real-time constraints and must rapidly generate collision-free, near-optimal and curvature-continuous feasible flight paths within a limited computational window. Although mainstream bidirectional RRT-based algorithms improve the basic search speed through parallel dual-tree expansion, they still suffer from inherent limitations, including blind sampling, fixed expansion strategies and poor environmental adaptability. To address these limitations, this study proposes a Dynamic Hybrid Multi-strategy RRT (DHM-RRT*) algorithm. In the sampling stage, a hybrid strategy combining frontier-density adaptive sampling, Halton low-discrepancy sampling and uniform random sampling is adopted. In the expansion stage, a four-level progressive expansion mechanism is designed, comprising goal-directed expansion, dual-distance scoring tangent-cone obstacle avoidance, improved artificial-potential-field guidance and random fallback expansion. The failure rate of each strategy is estimated online using an exponential moving average, and the expansion probabilities are dynamically and adaptively assigned. After path generation, path quality is further improved through greedy direct connection near the stitching seam and B-spline smoothing. The algorithm was independently evaluated in three MATLAB three-dimensional obstacle environments and compared with the best-performing baseline algorithm in each environment. The proposed algorithm reduced the average path length by 1.78%, 0.42% and 5.49%, respectively, and reduced the planning time by 38.89%, 34.78% and 29.03%, respectively. The simulation results demonstrate that the proposed algorithm provides clear advantages in convergence speed, path length, smoothness and environmental robustness under complex obstacle constraints.