Earthwork Volumetrics with Unmanned Aerial Vehicles A Comparative

Earthwork Volumetrics with Unmanned Aerial Vehicles A Comparative Study Raid Al-Tahir and Travis Barran Geomatics Engineering and Land Management, The University of the West Indies, Trinidad and Tobago ICon. ETech-2020, Faculty of Engineering, The UWI, St. Augustine, Trinidad and Tobago

Unmanned Aerial Vehicles • UAV is an aircraft operated with no pilot on board • Navigates manually, semi- or fully autonomous • Commonly referred to as: • • • UAV (Unmanned Aerial Vehicle) UAS (Unmanned Aerial System) RPAS (Remotely Piloted Aircraft System) s. UAV (Small UAV) Drone • “UAS” comprises of 3 or more main features: • Unmanned Aircraft / Air Vehicle • Command Control Link/ Data Link • Ground Control Station ICon. ETech-2020, Faculty of Engineering, The UWI, St. Augustine, Trinidad and Tobago

Global Interests in the UAV • UAVs have been around since the mid 1900 s • Over the past decade; • UAVs have become more widely used in civilian operations • UAV production has doubled and kept growing • Enhanced performance, payload, endurance and flexibility • Evolution of technology GNSS, gyroscopes, cameras • Development of algorithms for processing UAV images ICon. ETech-2020, Faculty of Engineering, The UWI, St. Augustine, Trinidad and Tobago

Some Reasons for the Popularity of UAV • Cost effective option and a return on investment. • Portable, easy to use, and customizable. • Quick deployment, data collection and data retrieval. • Use in high risk situations and inaccessible areas • Removing humans from dangerous locations • Minimise disruption of working site • Trucks and plant work uninterrupted • Less chance for site accidents ICon. ETech-2020, Faculty of Engineering, The UWI, St. Augustine, Trinidad and Tobago

Some Civilian Applications ICon. ETech-2020, Faculty of Engineering, The UWI, St. Augustine, Trinidad and Tobago

Earthwork Volumetric Calculations • Obtaining volumetric data for earthworks is an important task in many engineering disciplines • Highway/road construction, mining industry, . . • Currently used methods consists of: • Perform a topographic survey • Create two surfaces for before and after the earthwork activity, • Subtract one surface from the other to obtain the volume of material excavated or filled. • The volume measurements as traditionally executed • Use Total Station surveys, Global positioning system (RTK) • Labour intensive and fairly time consuming. ICon. ETech-2020, Faculty of Engineering, The UWI, St. Augustine, Trinidad and Tobago

UAV Photogrammetry for Volume Calculations • The constant advancements in UAV systems and automated photogrammetric software have made attaining geospatial data more cost effective and less time consuming. • The evolution of UAVs as measuring instruments has become attractive for many surveying applications in civil engineering. • The purpose of this investigation is to • analyse the performance of UAV systems in acquiring 3 D mapping data for earthmoving construction sites. • compare and assess the feasibility of UAV surveying to that of Total Station surveying. ICon. ETech-2020, Faculty of Engineering, The UWI, St. Augustine, Trinidad and Tobago

• A segment of the Churchill Roosevelt Highway Extension to Manzanilla (CRHEM) • East of the Cumoto road and passing through the Forest reserve • Along the west bound lane of the highway from chainages 7+380 to 7+460 (80 meters). • Width of the road section is 17. 45 meters. Thickness of the subbase layer • Test area: The finished sub grade level Test Area ICon. ETech-2020, Faculty of Engineering, The UWI, St. Augustine, Trinidad and Tobago

Data Acquisition and Pre-processing • Reconnaissance and Flight Planning • Establishing Ground Control Points • 9 GCPs for first flight along the road • 6 GCPs for the second mission • Acquisition of UAV Imagery • 159 vertical images in the first flight • 34 images in the second flight • Processing of UAV Imagery with Agisoft Photoscan Professional • A dense point cloud was generated: • 3, 889, 801 points for the subgrade • 19, 772, 696 points for the subbase ICon. ETech-2020, Faculty of Engineering, The UWI, St. Augustine, Trinidad and Tobago

Generating TIN Surfaces • Total Station-based surfaces • 27 points for the subgrade; • 25 points for subbase surfaces. • UAV-surface from point cloud • Point cloud was first filtered into 118, 364 points • A point in every 15 cm • ~4000 points between 4 TS points. ICon. ETech-2020, Faculty of Engineering, The UWI, St. Augustine, Trinidad and Tobago

Accuracy of UAV-Surfaces vs. Total Station’s • RMSE based on GCP: • Subgrade model: 0. 018 m in XY; 0. 008 m in Z • Subbase model: 0. 03 m in XY; 0. 004 m in Z • Point to Surface Comparison • Average Error: 0. 04 m • RMS Error: 0. 07 m • Difference in Volumes between methods Total UAV Difference % Diff. Station • Volumes UAV volume was larger than 743. 480 the Total Station’s because of 9. 26% the greater m 3 680. 290 62. 990 resolution of the surfaces used in the calculation. ICon. ETech-2020, Faculty of Engineering, The UWI, St. Augustine, Trinidad and Tobago

Required Time • Time difference for data collection • Total Station: 10 minutes to survey 1350 m² of the road section. • UAV: 10 minutes for to cover 24300 m² (6 Acres) in the first mission. • UAV: 3 minutes for 4050 m² (1 Acre) in the second flight. • Time difference for post processing • UAV processing lasted ~24 hours while the total station processing lasted just 8 minutes. • Time difference for Volume calculations • Volume from UAV data took longer time because of the larger number of points ICon. ETech-2020, Faculty of Engineering, The UWI, St. Augustine, Trinidad and Tobago

Cost Comparison Total Station Survey Cost (USD) UAV system Cost (USD) Leica TCR 405 $49, 000 DJI Mavic Pro $6, 950 2 Leica Prism $1, 400 Photoscan Pro $23, 800 2 Prism poles $1680 Autodesk Civil 3 D $14640 Total $66, 720 Total $30, 750 • UAV approach costs less than 50% of the cost for the Total Station approach ICon. ETech-2020, Faculty of Engineering, The UWI, St. Augustine, Trinidad and Tobago

Conclusion • The UAV approach was proven to be a more cost and time effective solution when compared to Total Station surveying in measuring the structural layers in road construction. • The achieved 4– 8 millimetre accuracy in the elevation of extracted surfaces are well within the allowable range. • UAV measurements provide a more accurate earth volume estimate since collecting more points than with the Total Station • UAV approach costs less than 50% of the cost for the Total Station approach • UAV allows for faster data collection over larger areas while allowing construction work to continue during data capture. Thank you Raid Al-Tahir and Travis Barran raid. altahir@sta. uwi. edu ICon. ETech-2020, Faculty of Engineering, The UWI, St. Augustine, Trinidad and Tobago