Robotics Institute, University of Michigan, Ann Arbor, MI 48109, USA.
Aerospace Engineering, University of Michigan, Ann Arbor, MI 48109, USA.
Sensors (Basel). 2021 Sep 23;21(19):6351. doi: 10.3390/s21196351.
Magnetometers measure the local magnetic field and are present in most modern inertial measurement units (IMUs). Readings from magnetometers are used to identify Earth's Magnetic North outdoors, but are often ignored during indoor experiments since the magnetic field does not behave how most expect. This paper presents methods to create, validate, and visualize three-dimensional magnetic field maps to expand the use of magnetic fields as a sensing modality for navigation. The utility of these maps is measured in their ability to accurately represent the magnetic field and to enable dynamic attitude estimation. In experiments with motion capture truth data, a small multicopter with three-axis inertial measurements, including magnetometer, traversed five flight profiles distinctly exciting roll, pitch, and yaw motion to provide interesting trajectories for attitude estimation. Indoor experimental results were compared to those outdoors to emphasize how spatial variation in the magnetic field drives the need for our mapping techniques. Our work presents a new way of visualizing 3D magnetic fields, which allows users to better reason about the magnetic field in their workspace. Next, we show that magnetic field maps generated from coverage patterns are generally more accurate, but training such maps using observations from desired flight paths is sufficient in the vicinity of these paths. All training sets were interpolated using Gaussian process regression (GPR), which yielded maps with <1 μT of error when interpolating between and extrapolating outside of observed locations. Finally, we validated the utility of our GPR-based maps in enabling attitude estimates in regions of high magnetic field spatial variation with experimental data.
磁力计测量局部磁场，存在于大多数现代惯性测量单元（IMU）中。磁力计的读数可用于在户外识别地球磁场的磁北极，但在室内实验中通常被忽略，因为磁场的行为方式与大多数人预期的不同。本文提出了创建、验证和可视化三维磁场图的方法，以扩展磁场作为导航传感模式的使用。这些地图的效用通过其准确表示磁场和实现动态姿态估计的能力来衡量。在具有运动捕捉真实数据的实验中，一架带有三轴惯性测量的小型三旋翼飞行器，包括磁力计，穿过五个飞行剖面，明显激发了滚转、俯仰和偏航运动，为姿态估计提供了有趣的轨迹。将室内实验结果与室外结果进行比较，以强调磁场的空间变化如何驱动我们的映射技术的需求。我们的工作提出了一种可视化 3D 磁场的新方法，使用户能够更好地理解其工作空间中的磁场。接下来，我们表明，从覆盖模式生成的磁场图通常更准确，但在这些路径附近，使用期望飞行路径的观测来训练这些地图就足够了。所有训练集都使用高斯过程回归（GPR）进行插值，在观测位置之间插值和外推时，产生的地图误差小于 1 μT。最后，我们使用实验数据验证了我们基于 GPR 的地图在高磁场空间变化区域中实现姿态估计的效用。
