Abstract
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.
Highlights
Three‐dimensional (3D) mapping is described as the process of gathering loca‐ tional information and possibly the attributes of features such as roads and buildings, and the representation of such in three dimensions that can be interpreted by a user [1]
This study conducted at the University of Lagos has shown that unmanned aerial vehicles (UAVs) have the ability to cover the large gap between terrestrial and aerial methods of mapping and data acquisition
The acquired and processed data from the flight mission can be utilised for different purposes, such as change detection analysis for land use/land cover, terrain modelling and infrastructural planning and monitoring
Summary
Three‐dimensional (3D) mapping is described as the process of gathering loca‐ tional information and possibly the attributes of features such as roads and buildings, and the representation of such in three dimensions (latitude, longitude and height above sea level) that can be interpreted by a user [1]. Conventional mapping tech‐ niques include triangulation, trilateration, traversing, levelling, and radiation [3, 4], while modern techniques include total station surveying, aerial photogrammetry, Global Positioning Systems (GPS) or Global Navigation Satellite Systems (GNSS) surveys, and remote sensing (RS) [5]. Measurements done in one image can only give two‐dimensional (2D) coordinates, while 3D coordinates can be obtained using two or more images of the same object, captured from differ‐ ent positions. This is called stereoscopic viewing or stereo photogrammetry [7]. Unmanned Aerial Vehicle (UAV) surveys have emerged as an alternative to the classical manned aerial photogrammetric surveys [1]
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