Assessing the Accuracy of Digital Surface Models Derived from Optical Imagery Acquired with Unmanned Aerial Systems

Salvatore Manfreda,Jana Mullerova,Sorin Herban,Matthew Perks,Pietro Vuono,Petr Dvorak,José Arranz Justel

doi:10.3390/drones3010015

Abstract

Small unmanned aerial systems (UASs) equipped with an optical camera are a cost-effective strategy for topographic surveys. These low-cost UASs can provide useful information for three-dimensional (3D) reconstruction even if they are equipped with a low-quality navigation system. To ensure the production of high-quality topographic models, careful consideration of the flight mode and proper distribution of ground control points are required. To this end, a commercial UAS was adopted to monitor a small earthen dam using different combinations of flight configurations and by adopting a variable number of ground control points (GCPs). The results highlight that optimization of both the choice and combination of flight plans can reduce the relative error of the 3D model to within two meters without the need to include GCPs. However, the use of GCPs greatly improved the quality of the topographic survey, reducing error to the order of a few centimeters. The combined use of images extracted from two flights, one with a camera mounted at nadir and the second with a 20° angle, was found to be beneficial for increasing the overall accuracy of the 3D model and especially the vertical precision.

Highlights

Digital surface models (DSMs) are traditionally delivered using terrestrial or aerial surveys, which are often time-consuming, difficult to organize, and costly [1]
The results of the quality assessment based on individual flights with different settings (Figure 3). Their combinations are summarized in Table 2, where we report the Root Mean Square Error (RMSE) estimated between the DSM raster model derived by the SfM-multi-view stereo (MVS) algorithms of Agisoft PhotoScan and the 16 check points distributed in the area
The literature offers a wide range of applications for the operational use of Unmanned Aerial Systems (UASs) for 3D model reconstruction based on SfM-MVS algorithms, offering different strategies aimed at minimizing the errors of these 3D models

Summary

Introduction

Digital surface models (DSMs) are traditionally delivered using terrestrial or aerial surveys (e.g., aerial photogrammetry and laser scanning), which are often time-consuming, difficult to organize, and costly [1]. Aerial photogrammetry has significantly advanced DSMs with the introduction of the new global position system (GPS) and digital camera technology that have led to reduced costs and increased efficiency [2,3,4,5]. UASs equipped with GPS and optical cameras are low-cost alternatives to the classical manned aerial photogrammetry in the short- and close-range domain applications [7]. The introduction of a user-friendly photogrammetric technique, called Structure-from-Motion (SfM), has produced a significant revolution in the field, where any researcher or technician can afford high-resolution topographic reconstruction for even low-budget research and applications [8]. SfM produces orthoimagery and digital surface/elevation models (DSM/DEMs) with very high spatial resolution in the order of centimeters [9,10], which is crucial for many applications, especially for change detection studies [11,12]

Methods

Discussion

Conclusion