In this article we propose a new online multiresolution path planning algorithm for a small unmanned air vehicle (UAV) with limited on-board computational resources. The proposed approach assumes that the UAV has detailed information of the environment only in the vicinity of its current position. Information about far away obstacles is also available, albeit with less accuracy. The proposed algorithm uses an integer arithmetic implementation of the fast lifting wavelet transform (FLWT) to get a multiresolution cell decomposition of the environment, whose dimension is commensurate to the onboard computational resources. A topological graph representation of the multiresolution cell decomposition is constructed efficiently, directly from the approximation and detail wavelet coefficients. Hardware-in-the-loop simulation (HILS) results validate the applicability of the algorithm on a small UAV autopilot. Comparisons with the standard D * -lite algorithm are also presented.
I. INTRODUCTIONAutonomous operation of UAVs requires both trajectory design (planning) and trajectory tracking (control) tasks to be completely automated. Given the short response time scales of modern aerial vehicles, on-board, real-time path planning is particulary challenging for small UAVs, which may not have the on-board computational capabilities (e.g. CPU and memory) to implement some of the sophisticated path planning algorithms developed in the literature.In a typical mission of a UAV, various sensors (e.g., cameras, radars, laser scanners, satellite imagery) having different range and resolution characteristics are employed to collect information about the environment the vehicle operates in. A computationally efficient path planning algorithm, specifically adopted for on-line implementation, should therefore choose the expedient information from all these sensors, and utilize the on-board computational resources on the part of the path (spatial and temporal) that needs it most. In a nutshell, a computationally efficient algorithm suitable for on-line implementation should be characterized by a combination of short term tactics (reaction to unforeseen threats) with long-term strategy (planning towards the ultimate goal).Multiresolution analysis is widely used in practice to mitigate the computational overhead in numerically costly applications, for example, computer graphics, using progressive, view-dependent, meshes [4]. The application of multiresolution methods to path planning problems is relatively recent. In [1], [13] multiresolution, hierarchical algorithms were used to alleviate the computational burden associated