Studies on Three-Dimensional (3D) Accuracy Optimization and Repeatability of UAV in Complex Pit-Rim Landforms As Assisted by Oblique Imaging and RTK Positioning.

Rui Bi,Lin Hu,Xiping Yuan,Raobo Li,Weidong Luo,Shu Gan,Sha Gao

doi:10.3390/s21238109

Rui Bi, Lin Hu + Show 5 more

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https://doi.org/10.3390/s21238109

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Abstract

Unmanned Aerial Vehicles (UAVs) are a novel technology for landform investigations, monitoring, as well as evolution analyses of long−term repeated observation. However, impacted by the sophisticated topographic environment, fluctuating terrain and incomplete field observations, significant differences have been found between 3D measurement accuracy and the Digital Surface Model (DSM). In this study, the DJI Phantom 4 RTK UAV was adopted to capture images of complex pit-rim landforms with significant elevation undulations. A repeated observation data acquisition scheme was proposed for a small amount of oblique-view imaging, while an ortho-view observation was conducted. Subsequently, the 3D scenes and DSMs were formed by employing Structure from Motion (SfM) and Multi-View Stereo (MVS) algorithms. Moreover, a comparison and 3D measurement accuracy analysis were conducted based on the internal and external precision by exploiting checkpoint and DSM of Difference (DoD) error analysis methods. As indicated by the results, the 3D scene plane for two imaging types could reach an accuracy of centimeters, whereas the elevation accuracy of the orthophoto dataset alone could only reach the decimeters (0.3049 m). However, only 6.30% of the total image number of oblique images was required to improve the elevation accuracy by one order of magnitude (0.0942 m). (2) An insignificant variation in internal accuracy was reported in oblique imaging-assisted datasets. In particular, SfM-MVS technology exhibited high reproducibility for repeated observations. By changing the number and position of oblique images, the external precision was able to increase effectively, the elevation error distribution was improved to become more concentrated and stable. Accordingly, a repeated observation method only including a few oblique images has been proposed and demonstrated in this study, which could optimize the elevation and improve the accuracy. The research results could provide practical and effective technology reference strategies for geomorphological surveys and repeated observation analyses in sophisticated mountain environments.

Highlights

As Unmanned Aerial Vehicles (UAVs) technology makes strides and is increasingly developed, UAVs have become progressively popularized and civilianized
UAVs equipped with a Real-Time Kinematic (RTK) system can capture images, and exploit differential correction data provided by Continuously Operating Reference Stations (CORS) to acquire high-precision positioning information [24] and achieve aerial triangulation without Ground Control Points (GCPs) [25,26]
The 3D scene accuracy assessment results for different datasets were analyzed using checkpoints (Table 4), which indicated that the magnitude of the plane error of the six datasets was consistent, whereas the magnitude of the elevation error was significantly different

Summary

Introduction

As UAV technology makes strides and is increasingly developed, UAVs have become progressively popularized and civilianized. As reported by existing studies, 3D scene construction achieved by exploiting images acquired by UAVs equipped with Global Navigation Satellite System (GNSS) with low positioning accuracy fails to meet 3D measurement accuracy requirements [15], and the achieved data results are of less significance to multi-phase geomorphological evolution analysis studies [16]. UAVs equipped with a Real-Time Kinematic (RTK) system can capture images, and exploit differential correction data provided by Continuously Operating Reference Stations (CORS) to acquire high-precision positioning information [24] and achieve aerial triangulation without GCPs [25,26]. When RTK UAVs are adopted to analyze the geomorphological evolution of long time series, the accuracy of the 3D scenes of repeated observations may change significantly. The repeated observation accuracy of RTK UAV has been rarely investigated, and its error analysis under no GCPs constraint has been scarce on the complex mountain environment terrain

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