In this correspondence, we consider a new unmanned aerial vehicle (UAV)-assisted oblique image acquisition system where a UAV is dispatched to take images of multiple ground targets (GTs). To study the three-dimensional (3D) UAV trajectory design for image acquisition, we first propose a novel UAV-assisted oblique photography model, which characterizes the image resolution with respect to the UAV's 3D image-taking location. Then, we formulate a 3D UAV trajectory optimization problem to minimize the UAV's traveling distance subject to the image resolution constraints. The formulated problem is shown to be equivalent to a modified 3D traveling salesman problem with neighbourhoods, which is NP-hard in general. To tackle this difficult problem, we propose an iterative algorithm to obtain a high-quality suboptimal solution efficiently, by alternately optimizing the UAV's 3D image-taking waypoints and its visiting order for the GTs. Numerical results show that the proposed algorithm significantly reduces the UAV's traveling distance as compared to various benchmark schemes, while meeting the image resolution requirement.

中文翻译：

---

无人机辅助倾斜图像采集的3D轨迹设计

在这种对应关系中，我们考虑了一种新型的无人机（UAV）辅助倾斜图像采集系统，在该系统中，UAV被派去拍摄多个地面目标（GT）的图像。为了研究用于图像采集的三维（3D）UAV轨迹设计，我们首先提出了一种新颖的UAV辅助斜摄影模型，该模型描述了有关UAV 3D图像拍摄位置的图像分辨率。然后，我们制定了一个3D无人机轨迹优化问题，以在图像分辨率约束下最小化无人机的行进距离。公式化问题显示为与带邻域的经过修改的3D旅行推销员问题等效，该问题通常是NP难的。为解决这一难题，我们提出了一种迭代算法，可以有效地获得高质量的次优解决方案，通过交替优化无人机的3D图像拍摄航点和GT的访问顺序。数值结果表明，与各种基准方案相比，该算法大大降低了无人机的行进距离，同时满足了图像分辨率的要求。