The developments in lightweight unmanned aerial vehicles (UAVs) and structure-from-motion (SfM)-based software have opened a new era in 3D mapping which is notably cost-effective and fast, though the photogrammetric blocks lead to systematic height error due to inaccurate camera calibration parameters particularly when the ground control points (GCPs) are few and unevenly distributed. The use of onboard Global Navigation Satellite System (GNSS) receivers (such as RTK- or PPK-based devices which use the DGNSS technique) to obtain the accurate coordinates of camera perspective centres has reduced the need for ground surveys, nevertheless, the aforementioned systematic error was reported in the UAV photogrammetric blocks. In this research, three flight-planning scenarios with oblique imagery in addition to the traditional nadir block were evaluated and processed with four different processing cases. Therefore, 16 various blocks with different overlaps, direct and indirect georeferencing approaches as well as flight-planning scenarios were tested to examine and offer the best imaging network. The results denote that the combination of oblique images located on a circle in the centre of the block with the nadir block provides the best self-calibration functionality and improves the final accuracy by 50% (from 0.163 to 0.085 m) for direct georeferenced blocks and by 40% (from 0.042 to 0.026 m) for indirect georeferenced blocks.

中文翻译：

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倾斜图像和飞行计划场景对无人机 3D 测绘精度的影响

轻型无人机 (UAV) 和基于运动结构 (SfM) 的软件的发展开启了 3D 测绘的新时代，尽管摄影测量块由于以下原因导致系统高度误差，但其成本效益显着且速度快。相机校准参数不准确，特别是当地面控制点 (GCP) 很少且分布不均匀时。使用机载全球导航卫星系统（GNSS）接收器（例如使用 DGNSS 技术的基于 RTK 或 PPK 的设备）来获取相机视角中心的精确坐标已经减少了地面测量的需要，然而，上述系统无人机摄影测量块报告错误。在这项研究中，除了传统的最低点块之外，还使用倾斜图像的三种飞行计划场景通过四种不同的处理案例进行了评估和处理。因此，我们对 16 个具有不同重叠、直接和间接地理参考方法以及飞行计划场景的不同块进行了测试，以检查并提供最佳的成像网络。结果表明，位于块中心圆上的倾斜图像与最低点块的组合提供了最佳的自校准功能，并将直接地理参考块的最终精度提高了 50%（从 0.163 到 0.085 m），对于间接地理参考块，提高了 40%（从 0.042 到 0.026 m）。