Millimeter wave radar can measure distances, directions, and Doppler velocity for objects in harsh conditions such as fog. The 4D imaging radar with both vertical and horizontal data resembling an image can also measure objects' height. Previous studies have used 3D radars for ego-motion estimation. But few methods leveraged the rich data of imaging radars, and they usually omitted the mapping aspect which is affected by the radar multipath returns, thus leading to inferior odometry accuracy. This paper presents a real-time imaging radar inertial odometry and mapping method, iRIOM, based on the submap concept. To fend off moving objects and multipath reflections, the iteratively reweighted least squares method is used for getting the ego-velocity from a single scan. To measure the agreement between sparse non-repetitive radar scan points and submap points, the distribution-to-multi-distribution distance for matches is adopted. The ego-velocity, scan-to-submap matches are fused with the 6D inertial data by an iterative extended Kalman filter to get the platform's 3D position and orientation. A loop closure module is also developed to curb the odometry module's drift. To our knowledge, iRIOM based on the two modules is the first 4D radar inertial SLAM system. On our and third-party data, we show iRIOM's favorable odometry accuracy and mapping consistency against the FastLIO-SLAM and the EKFRIO. Also, the ablation study reveal the benefit of inertial data versus the constant velocity model, the scan-to-submap matching versus the scan-to-scans matching, and loop closure.
翻译:毫米波雷达可以在恶劣条件下,例如雾中,测量物体的距离、方向和多普勒速度。具有垂直和水平数据的4D成像雷达还可以测量物体的高度。以前的研究使用3D雷达进行自我运动估计。但是很少有方法利用成像雷达的丰富数据,它们通常忽略了由雷达多路径返回影响的建图方面,从而导致较差的测速精度。本文提出了一种基于子地图概念的实时成像雷达惯性测速及建图方法iRIOM。为了抵御移动物体和多路径反射,使用迭代重加权最小二乘法从单个扫描中获取自我速度。采用分布到多分布距离来衡量稀疏、不重复雷达扫描点和子地图点之间的一致性。通过迭代扩展卡尔曼滤波器将自我速度、扫描到子地图的匹配与6D惯性数据融合以获取平台的3D位置和方向。还开发了一个循环闭合模块来抑制测速模块的漂移。据我们所知,基于这两个模块的iRIOM是第一个4D雷达惯性SLAM系统。在我们和第三方数据上,我们展示了iRIOM对比FastLIO-SLAM和EKFRIO的优越测速精度和建图一致性。另外,消融研究揭示了惯性数据相对于常速模型、扫描到子地图匹配相对于扫描到扫描匹配以及循环闭合的效益。