A Low Cost UWB Based Solution for Direct Georeferencing UAV Photogrammetry

Andrea Masiero,Antonio Vettore,Francesca Fissore

doi:10.3390/rs9050414

Abstract

Thanks to their flexibility and availability at reduced costs, Unmanned Aerial Vehicles (UAVs) have been recently used on a wide range of applications and conditions. Among these, they can play an important role in monitoring critical events (e.g., disaster monitoring) when the presence of humans close to the scene shall be avoided for safety reasons, in precision farming and surveying. Despite the very large number of possible applications, their usage is mainly limited by the availability of the Global Navigation Satellite System (GNSS) in the considered environment: indeed, GNSS is of fundamental importance in order to reduce positioning error derived by the drift of (low-cost) Micro-Electro-Mechanical Systems (MEMS) internal sensors. In order to make the usage of UAVs possible even in critical environments (when GNSS is not available or not reliable, e.g., close to mountains or in city centers, close to high buildings), this paper considers the use of a low cost Ultra Wide-Band (UWB) system as the positioning method. Furthermore, assuming the use of a calibrated camera, UWB positioning is exploited to achieve metric reconstruction on a local coordinate system. Once the georeferenced position of at least three points (e.g., positions of three UWB devices) is known, then georeferencing can be obtained, as well. The proposed approach is validated on a specific case study, the reconstruction of the façade of a university building. Average error on 90 check points distributed over the building façade, obtained by georeferencing by means of the georeferenced positions of four UWB devices at fixed positions, is 0.29 m. For comparison, the average error obtained by using four ground control points is 0.18 m.

Highlights

The use of Unmanned Aerial Vehicles (UAVs) is becoming more and more frequent all over the world
Despite the fact that portability is a key factor in the current success of these devices, it comes with restrictions on the admissible payload [6]: this implies a careful election of the instrumentation mounted in the UAV
Positioning and navigation are typically achieved by using lightweight Global Navigation Satellite System (GNSS) receivers and Micro-Electro-Mechanical System (MEMS)-embedded sensors (i.e., integrated use of GNSS and the Inertial Navigation System (INS) [7,8]); Remote Sens. 2017, 9, 414; doi:10.3390/rs9050414

Summary

Introduction

The use of Unmanned Aerial Vehicles (UAVs) is becoming more and more frequent all over the world. Eased by the availability of low cost systems, the number of UAV applications is ever, growing in the last decade [1,2,3]. A number of factors (the affordable cost, the advantageous portability, limited size and weight, the possibility of flying over areas difficult to reach on the ground, the ability to quickly acquire a quite large amount of information of a relatively large area while still ensuring the possibility of quite close views, if needed) makes UAVs an attractive monitoring and surveying instrument in a wide range of conditions. Comprehensive reviews of the state of the art for UAV applications, positioning strategies and imaging sensors can be found in [4,5] and in the references therein. Positioning and navigation are typically achieved by using lightweight Global Navigation Satellite System (GNSS) receivers and Micro-Electro-Mechanical System (MEMS)-embedded sensors (i.e., integrated use of GNSS and the Inertial Navigation System (INS) [7,8]); Remote Sens. 2017, 9, 414; doi:10.3390/rs9050414 www.mdpi.com/journal/remotesensing

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