An Accuracy Comparison between GPS Surveying and UAV Surveying on Seawall Monitoring

Photogrammetry has been utilised for a significant amount of time, originally being use by the military as renaissance surveys to capture information in the field. This technology has science has now progressed and is now used within the field of surveying for spatial solutions, such as Digital Surface Models (DSM) and monitoring surveys. With the introduction of small, cheap, Unmanned Aerial Systems (UAS) in more recent years, and the technology in GPS equipment and satellites available becoming ever more reliable, it makes the surveyor question, what kind of accuracy can we achieve with UAS and is it comparable to that of the GPS? This paper focuses on a comparison of accuracy between conventional Cors RTK GPS System and the commercial based UAS photogrammetry data from a DJI Phantom 4 Drone. These systems are becoming more and more common within the work area and have become significantly more advanced but also significantly cheaper. The UAS platform (DJI Phantom 4) has all the capabilities to perform a photogrammetric survey, tethered with in-house mission planning programs such as litchi, this gives the drone and user full autonomous capabilities and to create a flight path with the ample amount of overlap required to create an accurate 3D model of the project area. This paper will compare the data sets collected between the GPS survey and the UAS survey completed to analyse the accuracies between the two and whether this method of surveying can accurate monitor a sea wall and the movements that may occur. The accuracy can be illustrated between the two types of survey through the use of a statistical analyse of the data creating a confidence interval expressed in the form of RMSEx, RMSEy and RMSExy. This method will also be used to check the accuracy between the two types in relation to elevation, thus ensure all three dimensions of error are checked, with hopefully similar results being obtained between the two. Photogrammetry, more so UAS, will change the survey industry. As technology continues to advance so will the methods in which data can be captured and the cameras used, this will enable the user a much more accurate result, creating better solutions and more project opportunities into the future. However with the standard of UAS or drones currently available in the market and within the price range of a DJI Phantom 4, it would of best practice to limit the range of data that is captured and the accuracies in which are required. Currently the accuracy of the UAS or drone is limited by many factors, but it would be best practice to assume the drone is accurate to +/- 30mm in distance and +/- 50mm in elevation. Although the results of this project satisfied the aim of this project, it is recognized that these results can be improved by alternative methods mentioned in the discussion section of the report and as well as number of recommendations for future research to better understand the limitations of these systems in providing spatial data