Due to high computation demand, slant total delays (STDs) determined by 3D ray tracing cannot be widely used in geodetic analysis. This study proposes a novel fast 3D ray tracing approach, named APM-3D, based on piecewise algorithm and strictly matched step size. It can produce more than 1000 rays per second with a single core PC, which satisfies the operational applications of slant delays in mapping function establishment and other areas. Comparisons have shown mm-level agreement in slant delays at 5° elevation angle between APM-3D and several algorithms presented by different institutes in a comparison campaign. APM-3D also exhibits better stability than the standard RK4 method. Further validation using a 3D ray tracing based on the Cartesian coordinate system and 2D ray tracing also indicates excellent agreement, while constant differences in geometric delays between 3 and 2D exist under complex weather conditions. With ERA5 reanalysis data, the characteristics of STD evolution are presented during a rainstorm that occurred on July 1–2, 2020, over Wuhan.

由于高计算需求，由 3D 射线追踪确定的倾斜总延迟 (STD) 不能广泛用于大地测量分析。本研究提出了一种基于分段算法和严格匹配步长的新型快速 3D 光线追踪方法，称为 APM-3D。单核PC每秒可产生1000多条光线，满足在建图功能建立等领域的斜延迟操作应用。比较表明，APM-3D 与不同机构在比较活动中提出的几种算法之间在 5° 仰角处的倾斜延迟具有毫米级一致性。APM-3D 还表现出比标准 RK4 方法更好的稳定性。使用基于笛卡尔坐标系的 3D 射线追踪和 2D 射线追踪的进一步验证也表明非常一致，而在复杂的天气条件下，3D 和 2D 之间的几何延迟存在恒定差异。ERA5 再分析数据显示了 2020 年 7 月 1 日至 2 日发生在武汉上空的暴雨期间的 STD 演变特征。