RTK GNSS-Assisted Terrestrial SfM Photogrammetry without GCP: Application to Coastal Morphodynamics Monitoring

Marion Jaud,Stéphane Bertin,Christophe Delacourt,Mickaël Beauverger,Emmanuel Augereau

doi:10.3390/rs12111889

Abstract

The present article describes a new and efficient method of Real Time Kinematic (RTK) Global Navigation Satellite System (GNSS) assisted terrestrial Structure-from-Motion (SfM) photogrammetry without the need for Ground Control Points (GCPs). The system only requires a simple frame that mechanically connects a RTK GNSS antenna to the camera. The system is low cost, easy to transport, and offers high autonomy. Furthermore, not requiring GCPs enables saving time during the in situ acquisition and during data processing. The method is tested for coastal cliff monitoring, using both a Reflex camera and a Smartphone camera. The quality of the reconstructions is assessed by comparison to a synchronous Terrestrial Laser Scanner (TLS) acquisition. The results are highly satisfying with a mean error of 0.3 cm and a standard deviation of 4.7 cm obtained with the Nikon D800 Reflex camera and, respectively, a mean error of 0.2 cm and a standard deviation of 3.8 cm obtained with the Huawei Y5 Smartphone camera. This method will be particularly interesting when simplicity, portability, and autonomy are desirable. In the future, it would be transposable to participatory science programs, while using an open RTK GNSS network.

Highlights

Coastal monitoring requires repeated surveys combining very high spatial resolution and short revisit times, or high reactivity after morphogenesis events, in order to understand the processes driving shoreline evolution and to measure sediment transfers
The mean error comparing the Geotagged SfM point cloud to the Terrestrial Laser Scanner (TLS) mesh is 2.13 m with a standard deviation of 1.22 m. For estimating this error, CloudCompare® measures the normal distance between a point and the closest facet on the TLS mesh, even if it does not correspond to the same portion of the cliff
The difference between the Geotagged SfM point cloud and the TLS point cloud was assessed by performing an automatic registration in CloudCompare®, which is based on an Iterative Closest Point (ICP) algorithm

Summary

Introduction

Coastal monitoring requires repeated surveys combining very high spatial resolution and short revisit times, or high reactivity after morphogenesis events, in order to understand the processes driving shoreline evolution and to measure sediment transfers. In this context, the development of close-range remote-sensing methods during the last decades has provided an opportunity to create Digital Elevation Models (DEMs) at low cost and meeting the need in accuracy, resolution, and flexibility of acquisition.

Methods

Results

Discussion

Conclusion