Parametric Path Planning for Autonomous Ships in Spatially Constrained Waterways

Autonomous ship navigation in maritime environments requires a flexible approach for path planning to avoid obstacles, ensure regulatory compliance, and increase efficiency by introducing constraints on planned routes. Traditional grid-based methods, such as A*, require a discretisation that inherently fixes the path resolution to the scale of the area and the complexity of spatial features. Over large geographic areas, this resolution may be insufficient to capture complex navigation requirements, resulting in sub-optimal and potentially inaccurate paths. To address this problem, we propose a parameterized path-planning algorithm that accounts for navigable areas and obstacles represented in continuous space using, e.g., polygons derived from electronic navigational charts. The algorithm starts by generating a straight-line path between the start and end points and dividing it into equal segments. At each segment, perpendicular lines are drawn, and points are iteratively sampled along them. These sampled points are connected across segments to form a network of possible paths. The optimal path is then selected based on parameterisation strategies such as minimising the total distance or the sum of consecutive angles. This approach eliminates the need for grid-based discretisation, making it well-suited to large-scale navigation with varying degrees of complexity along the path. To demonstrate the applicability of our approach, we compare it with traditional path planning algorithms in a variety of maritime navigation scenarios. We have developed a benchmark suite based on real-world challenges, including constrained port approaches, complex inland waterways with narrow passages, and open sea navigation. These scenarios include a range of operational constraints such as manoeuvring in busy areas, avoiding shallow water, and transitions from open water to complex harbour layouts. By evaluating performance under these different conditions, we ensure that our approach is robust and adaptable to different maritime environments.