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Validating Uav-Sfm Photogrammetry Heights for Highway Topographic Surveying in Tanzania
Abstract
The demand for accurate topographic surveying data to support ever-growing infrastructural development such as highway construction is huge. Topographic surveying defines a point with X, Y, and Z relative values to create a 3D earth surface model. The Z values represent the vertical height of a point from the benchmark. Vertical heights can be obtained from conventional levelling and Digital Elevations Models (DEMs), as in the case of heights from unmanned aerial vehicle structures from motion photogrammetry (SfM-P) and global navigation satellite systems (GNSSs).
GNSS-Real Time Kinematics (RTK) is the most common method used but is sometimes outscored because of limitations in terms of time consumption and physically inaccessible surfaces. Recently, SfM-P surveys appear to have been quick and effective in accessing areas that would not have been possible when applying GNSS RTK methods. SfM-P surveys have recently been reorganized through cheap, rapid and elementary methods, but few research findings have been documented. Therefore, the study for validating SfM-P surveys in topographic surveys of highways in Tanzania has proved to be most opportune.
In this study, an evaluation was performed by comparing SfM-P survey method heights to GNSS RTK method heights for an area with 3km wide and 19 km long. A total of 39 ground control points was used. The standard deviation between the SfM-P method heights and the GNSS RTK method heights was ±1.4 cm. The samples of elevation data for the preliminary surveying of highways were determined at an 80% accuracy level. However, among the respective heights, only 20% produced a +/- two-centimetre (2 cm) relative precision ─- an extremely high precision level and most satisfactory for detailed topographic surveys. This study confirms that the SfM-P survey can be most helpful in preliminary highway surveys in Tanzania and in surveys of those areas, such as the Dodoma region, with a sparser vegetation cover. However, the SfM-P survey method cannot guarantee good performance to comply with the detailed highway topographic survey height requirements of Tanzania.
