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 developed an MPC-based formation controller. We performed 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/ku9wxfpu and video of our method is provided https://tinyurl.com/yncez2cy.

翻译：针对自然栖息地中动物的跟踪与运动捕捉，一组安全且静音的天空平台（如搭载摄像头的飞艇）非常适用。在前期工作中，我们推导了最优运动捕捉的编队特性，包括保持观察者相对于目标的恒定角间距、阈值距离以及使目标始终位于相机视图中心。与多旋翼飞行器不同，飞艇具有非完整性约束且受环境风影响，其朝向与飞行方向紧密耦合。因此，假设运动方向与朝向独立的多旋翼控制方案并不适用。本文通过首先利用飞艇空速与其到目标距离之间的周期关系来解决该问题，基于此推导出满足最优运动捕捉编队特性的解析解与数值解，并开发了基于模型预测控制的编队控制器。我们对解算方法、适用边界条件进行了理论分析，开展了大量仿真实验，并利用无人飞艇进行了实际展示。开源代码（https://tinyurl.com/ku9wxfpu）及方法演示视频（https://tinyurl.com/yncez2cy）已提供。