Authors: Salar Khudhur Hussein1 & Kamal Yaseen Abdulla2
1Civil Engineering Department, Technical College, Erbil Polytechnic University, Erbil, Iraq
2Civil Engineering Department, Technical College, Erbil Polytechnic University, Erbil, Iraq
Abstract: Today, advanced Global Navigation Satellite System (GNSS) receivers are improving the accuracy of positioning information, but in critical locations such as urban areas, places with big trees, high tension electric poles, marshes, high buildings, mountainous areas, and so on, the satellite availability is limited due to the signal blocking problem, which degrade the required accuracy. For this reason, different methods of measurement should be used.
The objective of this study is to evaluate and compare the precision, the accuracy, and the time expenditure of total station (TS), Global Positioning System (GPS), currently called (GNSS), (Static and Real Time Kinematic methods). Measurements will improve the knowledge about how much precision and accuracy can be achieved and at what time expense. To investigate this task, two Benchmarks (BMs) were established inside the campus of College of Technology Erbil polytechnic University (EPU) which are used as base lines for the establishment of a reference network consisted of 20 control points. Each point was measured five times by using Topcon 105 Total Station and served as a reference value for comparison with RTK-GNSS, GPS instrument. The data were processed from the instruments to a computer using different software according to the instruments used such as Topcon Tools v7, Trimble’s GNSS Net, GIS Map Source Version 6.4, and Leica geo office software.
The registration and geo-referencing (using Arc Map 10.2.2. software) process was performed to convert the scanned satellite images of the point cloud to combine scanned maps together in one coordinate system then transformed to World Geodetic System 1984 (WGS84).
According to the obtained results, the reference network points measured with TS were determined with Easting13mm, Northing 11mm and Elevation 15mm precisions for both horizontal and vertical coordinates. When using RTK-GNSS method on the same reference network points, which is expressed by RMSE, the accuracy obtained for easting was 8 mm, for northing was 10.6mm, and 8.4 mm in elevation has been achieved. The RTK-GNSS measurements, which were measured five times, determined with a maximum standard deviation of Easting 0.9 mm, Northing 0.96 mm and Elevation 0.93 mm for horizontal and vertical coordinates, respectively. The precision of the remaining control points is below these levels.
The Center line of the road (120m) was projected (set out) using TS, then the points were measured with RTK-GNSS. The maximum difference between both methods in Easting was 19mm, in the Northing was 22 mm and in the Elevation was 30 mm. So, the differences considered to be small as it was in acceptable range.
Keywords: Global Navigation Satellite System (GNSS), Total Station (TS), Accuracy, Precision, GIS
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