For tracking and motion capture (MoCap) of animals in their natural habitat, a formation of safe and silent aerial platforms, such as airships with on-board cameras, is well suited. In our prior work we derived formation properties for optimal MoCap, which include maintaining constant angular separation between observers w.r.t. the subject, threshold distance to it and keeping it centered in the camera view. Unlike multi-rotors, airships have non-holonomic constrains and are affected by ambient wind. Their orientation and flight direction are also tightly coupled. Therefore a control scheme for multicopters that assumes independence of motion direction and orientation is not applicable. In this paper, we address this problem by first exploiting a periodic relationship between the airspeed of an airship and its distance to the subject. We use it to derive analytical and numeric solutions that satisfy the formation properties for optimal MoCap. Based on this, we develop an MPC-based formation controller. We perform theoretical analysis of our solution, boundary conditions of its applicability, extensive simulation experiments and a real world demonstration of our control method with an unmanned airship. Open source code https://tinyurl.com/AsMPCCode and a video of our method is provided at https://tinyurl.com/AsMPCVid .

翻译：在自然栖息地中对动物进行跟踪与动作捕捉（MoCap）时，由搭载摄像头的安全静音空中平台（如飞艇）组成的编队尤为适用。我们先前的工作推导了最优动作捕捉的编队特性，包括保持观测者相对于目标之间恒定的角间距、距目标的临界距离，以及确保目标始终居于相机视野中心。与多旋翼飞行器不同，飞艇具有非完整约束并受环境风影响，其航向与飞行方向紧密耦合。因此，基于运动方向与航向独立性假设的多旋翼控制方案并不适用。本文首先利用飞艇空速与目标距离之间的周期关系，推导出满足最优动作捕捉编队特性的解析解与数值解。在此基础上，我们开发了基于模型预测控制（MPC）的编队控制器，并对所提解法的理论可行性、边界条件进行了分析，开展了大量仿真实验，并通过无人飞艇进行了实际场景验证。开源代码与演示视频分别见：https://tinyurl.com/AsMPCCode 与 https://tinyurl.com/AsMPCVid 。