Suggestions to Limit Geometric Distortions in the Reconstruction of Linear Coastal Landforms by SfM Photogrammetry with PhotoScan® and MicMac® for UAV Surveys with Restricted GCPs Pattern

Marion Jaud,Nicolas Le Dantec,Philippe Grandjean,Christophe Delacourt,Sophie Passot,Pascal Allemand

doi:10.3390/drones3010002

Abstract

Owing to the combination of technological progress in Unmanned Aerial Vehicles (UAVs) and recent advances in photogrammetry processing with the development of the Structure-from-Motion (SfM) approach, UAV photogrammetry enables the rapid acquisition of high resolution topographic data at low cost. This method is particularly widely used for geomorphological surveys of linear coastal landforms. However, linear surveys are generally pointed out as problematic cases because of geometric distortions creating a “bowl effect” in the computed Digital Elevation Model (DEM). Secondly, the survey of linear coastal landforms is associated with peculiar constraints for Ground Control Points (GCPs) measurements and for the spatial distribution of the tie points. This article aims to assess the extent of the bowl effects affecting the DEM generated above a linear beach with a restricted distribution of GCPs, using different acquisition scenarios and different processing procedures, both with PhotoScan® software tool and MicMac® software tool. It appears that, with a poor distribution of the GCPs, a flight scenario that favors viewing angles diversity can limit DEM’s bowl effect. Moreover, the quality of the resulting DEM also depends on the good match between the flight plan strategy and the software tool via the choice of a relevant camera distortion model.

Highlights

Computing Digital Elevation Models (DEM) at centimetric resolution and accuracy is of great interest for all geomorphological sciences [1]
As small Unmanned Aerial Vehicles (UAVs) allow the rapid acquisition of high resolution (
As reported in reference [7], SfM photogrammetry methods offer the opportunity to extract high resolution and accurate spatial data at very low-cost using consumer grade digital cameras that can be embedded on small UAVs

Summary

Introduction

Computing Digital Elevation Models (DEM) at centimetric resolution and accuracy is of great interest for all geomorphological sciences [1]. For high dynamic geomorphological processes (coastal or riverine environment for example), it is fundamental to collect accurate topographic data allowing the comparison of DEMs computed with images of successive campaigns in order to calculate a sediments budget, assess risks of erosion or flooding or initialize numerical models [2]. As reported in reference [7], SfM photogrammetry methods offer the opportunity to extract high resolution and accurate spatial data at very low-cost using consumer grade digital cameras that can be embedded on small UAVs. several articles highlight the fact that the reconstructed results may be affected by systematic broad-scale errors restricting their use [1,12,13,14]. It is helpful to propose some practical guidance to limit such geometric distortions

Objectives

Findings

Discussion

Conclusion