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Unmanned Aerial Vehicles for Three‑dimensional Mapping and Change Detection Analysis

Gbopa Adetola Olufunmilayo, Ayodele Emmanuel Gbenga, Okolie Chukwuma John, Ajayi Akinwumi Olaitan, Iheaturu Chima Jude

Geomatics and Environmental Engineering

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2021

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Vol. 15, no. 1

41--61

EN

Unmanned Aerial Vehicles (UAVs), commonly known as drones are increasingly being used for three dimensional (3D) mapping of the environment. This study utilised UAV technology to produce a revised 3D map of the University of Lagos as well as land cover change detection analysis. A DJI Phantom 4 UAV was used to collect digital images at a flying height of 90 m, and 75% fore and 65% side overlaps. Ground control points (GCPs) for orthophoto rectification were coordinated with a Trimble R8 Global Navigation Satellite System. Pix4D Mapper was used to produce a digital terrain model and an orthophoto at a ground sampling distance of 4.36 cm. The change detection analysis, using the 2015 base map as reference, revealed a significant change in the land cover such as an increase of 16,306.7 m2 in buildings between 2015 and 2019. The root mean square error analysis performed using 7 GCPs showed a horizontal and vertical accuracy of 0.183 m and 0.157 m respectively. This suggests a high level of accuracy, which is adequate for 3D mapping and change detection analysis at a sustainable cost.

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An assessment of the accuracy of structure-from-motion (SfM) photogrammetry for 3D terrain mapping

Iheaturu Chima Jude, Ayodele Emmanuel Gbenga, Okolie Chukwuma John

Geomatics, Landmanagement and Landscape

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2020

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no. 2

65--82

EN

Unmanned Aerial Vehicles (UAVs) equipped with photogrammetric or remote sensing instrumentations offer numerous opportunities in mapping and data collection for topographic modelling. An example is an emerging technique known as Structure-from-Motion (SfM) photogrammetry used for the collection of low-cost, high spatial resolution, three-dimensional data. This study utilised the real time kinematic-based point-to-point validation technique and two sets of randomly selected ground control points to assess the capability and geometric accuracy of SfM-technology for three-dimensional (3D) terrain mapping over a small study area to contribute to the knowledge of applicability. The data used was collected in Garscube Sports Complex, Glasgow City Council, Scotland. The study utilised fifteen (15) Ground Control Points (GCPs) coordinated by the Real Time Kinematic Global Navigation Satellite System (RTK GNSS) positioning technique, while a DJI Phantom 3 Professional unmanned aerial vehicle was used to obtain the aerial photos in a single flight to minimise cost. The processing of the photos was done using Pix4Dmapper Pro software version 4.2.27. A point-to-point validation method was used to evaluate the 3D positional accuracy of the orthophoto and DSM. The results of the validation with ten checkpoints suggest a high level of accuracy and acceptability given a Root Mean Square Error of 20.93 mm, 18.48 mm and 46.05 mm in the X, Y and Z coordinates respectively. In conclusion, the study has shown that SfM technique can be used to produce high-resolution and accurate topographic data for geospatial applications with significant advantages over the traditional methods. However, it is to be noted that the quality of the data captured is dependent on the methodology adopted and should be taken into consideration.

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An assessment of seasonal variations in the cref cors at the University of Lagos

Nwilo Peter Chigozie, Ayodele Emmanuel Gbenga, Okolie Chukwuma John, Orji Michael Joseph, Marve Mnguhenen Funmilayo, Oyelade Esther Abidemi, Daramola Olagoke Emmanuel

Geomatics, Landmanagement and Landscape

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2020

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no. 1

63--77

EN

Continuously Operating Reference Stations (CORS) are reference stations of the Global Navigation Satellite System (GNSS), providing fundamental positioning infrastructure that is accurate and reliable. As such, CORS are designed to meet the needs of a wide range of users requiring high three-dimensional (3D) positional accuracy. The Continuously Operating Reference Station at the Engineering Faculty (CREF), University of Lagos was set up in order to support research applications in Surveying, Mapping and Geodesy. This study evaluates the seasonal variations in the 3D coordinates of CREF using metrics such as coordinate differences, Standard Deviation (SD) and Standard Error (SE). The Canadian Spatial Reference System (CSRS), known as CSRS – Precise Point Positioning (CSRS-PPP) was used to compute the station’s daily coordinates over a three-year period from 2016 to 2018. In the analysis, the daily coordinates were divided into two seasons - the wet and the dry. The results obtained show that the dry and the wet seasons had SDs (5.4 mm, 3.9 mm, and 2.0 mm) and (5.2 mm, 18.6 mm and 14.4 mm) in the x, y and z-directions respectively. Generally, the dry season presents a better result than the wet season as revealed by the accuracy metrics. These results have led to an increased understanding of the seasonal variability inherent in the data acquired by GNSS CORS, and must be taken into consideration: in particular, for GNSS applications such as the weather prediction and water vapour estimation. This study concludes that more needs to be done regarding the maintenance of CREF to ensure data continuity and reliability for geodetic studies.