Evaluating the Potential of PPK Direct Georeferencing for UAV-SfM Photogrammetry and Precise Topographic Mapping

Abstract

Abstract. Images captured by Unmanned aerial vehicle (UAV) and processed by Structure from Motion (SfM) photogrammetry are increasingly used in geomorphology to obtain high resolution topography data. Conventional georeferencing using ground control points (GCPs) provides reliable positioning but the geometrical accuracy critically depends on the number and spatial layout of the GCPs. This limits the time- and cost-effectiveness. Direct georeferencing of the UAV images with differential GNSS, such as PPK (Post-Processing Kinematic), may overcome these limitations by providing accurate and directly georeferenced surveys. To investigate the positional accuracy, repeatability and reproducibility of digital surface models (DSMs) generated by a UAV-PPK-SfM workflow, we carried out multiple flight missions with different camera/UAV systems. Our analysis showed that the PPK solution provides the same accuracy (mean: ca. 0.01 m, RMSE: ca. 0.03 m) as the GCP method. Furthermore, our results indicated that camera properties (i.e., focal length, resolution, sensor quality) have an impact on the accuracy but planimetric and altimetric errors remained in the range of 0.011 to 0.024 m. By analysing the repeatability of DSM construction over a time period of a few months, our study demonstrates that a UAV-PPK-SfM workflow can provide consistent, repeatable 4D data with an accuracy of a few centimetres without the use of GCPs. An uncertainty analysis showed that the minimum level of topographical change detection was ca. ±0.04 m for a high-end DSLR camera and ca. ±0.08 m for an action camera (for a flight height of 45 m). The level of detection substantially improved when reducing the UAV flight height. This study demonstrates the repeatability, reproducibility and efficiency of a PPK-SfM workflow in the context of 4D earth surface monitoring with time-laps SfM photogrammetry. As such, it should be considered as an efficient tool to monitor geomorphic processes accurately and quickly at a very high spatial and temporal resolution.

A Test on the Potential of a Low Cost Unmanned Aerial Vehicle RTK/PPK Solution for Precision Positioning

“…Furthermore, since the PPK processing does not require GCPs (Ground Control Points), it is suitable for quite large areas and also shows different changes in topographical altitude. The mapping using PPK algorithms had the same accuracy as the method involving the use of GCPs [ 24 ].…”

“…The goodness of the GNSS data collected was verified, both as positions and as raw data and for both the Rover and the Bases. In particular, the RTKLIB [ 24 , 30 ] software was used for the QC (Quality Check) of the three different bases. For each acquisition, a satellite visibility analysis was carried out with the creation of Skyplot, Visibility Chart and SA/DOP (Satellite Availability/Dilution Of Precision).…”

Multiplatform-SfM and TLS Data Fusion for Monitoring Agricultural Terraces in Complex Topographic and Landcover Conditions

“…However, recording raw GNSS data is also desirable, as a backup in the case of radio link (i.e., between a master station and the UAV GNSS) problems, in order to refine the camera station positions (i.e., precise ephemeris data of GNSS satellites are available during postprocessing), and to consider the UAV trajectory and atmospheric error sources. Consequently, postprocessing kinematic (PPK) solution can often provide a more accurate solution than RTK [57,[63][64][65].…”

“…The UAV was fitted with a compact multi-GNSS RTK receiver (Emlid Reach M+, Emlid Ltd., Hong Kong; Tallysman TW2708 antenna model) with RTK-PPK capability to log the raw data as UBX format using global positioning system (GPS) and GLONASS satellites. The offset shift between the antenna phase center (placed on an aluminum plate, 22.5 cm right above the camera lens center) and camera projection center was considered during the postprocessing, assuming a constant vertical offset (more details can be found in [65], where the same system was used). Moreover, an electronic system was used to integrate and synchronize the GNSS with the action camera for image geotagging.…”

Kontribusi Global Navigation Satellite System Pada Penentuan Titik Kontrol Udara Di Metode Fotogrametri Unmanned Aerial Vehicle Untuk Pemetaan Skala Besar Di Indonesia

“…Metode penentuan posisi untuk proses direct georeferencing dapat menggunakan metode PPK (Zhang et al, 2019) maupun RTK (Forlani et al, 2018). Penentuan koordinat dengan Metode RTK maupun PPK menggunakan metode yang sama, yaitu diferensial GNSS.…”