Quality Assessment of DSMs Produced from UAV Flights Georeferenced with On-Board RTK Positioning

Gianfranco Forlani,Elisa Dall’Asta,Umberto Morra Di Cella,Fabrizio Diotri,Marina Santise,Riccardo Roncella

doi:10.3390/rs10020311

Gianfranco Forlani, Elisa Dall’Asta + Show 4 more

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https://doi.org/10.3390/rs10020311

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Abstract

High-resolution Digital Surface Models (DSMs) from unmanned aerial vehicles (UAVs) imagery with accuracy better than 10 cm open new possibilities in geosciences and engineering. The accuracy of such DSMs depends on the number and distribution of ground control points (GCPs). Placing and measuring GCPs are often the most time-consuming on-site tasks in a UAV project. Safety or accessibility concerns may impede their proper placement, so either costlier techniques must be used, or a less accurate DSM is obtained. Photogrammetric blocks flown by drones with on-board receivers capable of RTK (real-time kinematic) positioning do not need GCPs, as camera stations at exposure time can be determined with cm-level accuracy, and used to georeference the block and control its deformations. This paper presents an experimental investigation on the repeatability of DSM generation from several blocks acquired with a RTK-enabled drone, where differential corrections were sent from a local master station or a network of Continuously Operating Reference Stations (CORS). Four different flights for each RTK mode were executed over a test field, according to the same flight plan. DSM generation was performed with three block control configurations: GCP only, camera stations only, and with camera stations and one GCP. The results show that irrespective of the RTK mode, the first and third configurations provide the best DSM inner consistency. The average range of the elevation discrepancies among the DSMs in such cases is about 6 cm (2.5 GSD, ground sampling density) for a 10-cm resolution DSM. Using camera stations only, the average range is almost twice as large (4.7 GSD). The average DSM accuracy, which was verified on checkpoints, turned out to be about 2.1 GSD with the first and third configurations, and 3.7 GSD with camera stations only.

Highlights

Photogrammetric blocks flown by drones with on-board receivers capable of real-time kinematic (RTK) positioning do not need ground control points (GCPs), as camera stations at exposure time can be determined with cm-level accuracy, and used to georeference the block and control its deformations
This paper presents an experimental investigation on the repeatability of Digital Surface Models (DSMs) generation from several blocks acquired with a RTK-enabled drone, where differential corrections were sent from a local master station or a network of Continuously Operating Reference Stations (CORS)
Following a previous study by Benassi et al [39], the objective of this paper is to investigate a further step of the photogrammetric workflow in unmanned aerial vehicles (UAVs) blocks oriented by AAT, i.e., the repeatability and the accuracy of DSM generation

Summary

Introduction

In the past, specialised hardware and software, long processing times by trained personnel, high fixed costs, and limits in platform flexibility hampered or prevented the application of traditional airborne photogrammetry in many Earth science and engineering branches. The combination of SfM (structure from motion) photogrammetry [1] and unmanned aerial vehicle (UAV). Photogrammetry [2], i.e., of highly efficient software packages and great platform flexibility, supplies a very effective surface reconstruction tool, delivering DSM with unprecedented resolution at low cost. Getting rid of the sometimes awkward search for appropriate instrument setting locations, UAVs are taking a good deal of surveys that were thought to be the preserve of terrestrial laser scanning back to photogrammetry

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