Abstract
Currently, Global Positioning System (GPS) techniques are becoming a much larger part of the surveying industry. Many companies are now using GPS in their everyday work activities. The Real Time Kinematic (RTK) positioning is an integral part of topographic surveys, road surveying, constructions and most civil engineering applications. Normally, RTK can be used to collect the positioning data successfully and quickly. The civil and construction projects are designed in ground distances while RTK measurements are done in grid coordinate system, in which the distances between points are different from ground. The RTK measurements should be converted to ground for compatibility with the designed. In this paper, the accuracy of three alternatives for converting RTK measurements to ground was studied. These alternatives are, using scale factor, using two ground reference points and using Low Distortion Projection (LDP) surface. For the accuracy investigation purpose, a traverse of 14 points elongated for a distance of about 1400 m was constructed. Its coordinates were measured using total station, then the misclosure error was computed and the coordinates were adjusted. The traverse points coordinates were measured again using RTK_GPS considering one of them as base point. The three studied alternatives were applied and the results were compared. The results show that the accuracy of the three alternatives is ranging from 2.1 to 2.9 cm in the relative position of points to the base point. For absolute position accuracy, the two ground reference points alternative is the most accurate alternative with an average error of 3.8 cm while the other two alternatives are almost the same with an average error of 12.3 cm.
Highlights
The Real Time Kinematic (RTK) approach is a differential positioning technique that uses known coordinates of a reference station occupied by one receiver to determine coordinates of unknown points visited by a rover receiver [1]
Applying the Combination Factor to convert the grid distances to the ground ones, the errors were reduced to an average of 2.6 cm while the maximum error was 4.2 cm
Using two ground reference points to convert RTK distances to ground distances reduce the error to an average of 2.1 cm with a maximum error of 3.8 cm
Summary
The Real Time Kinematic (RTK) approach is a differential positioning technique that uses known coordinates of a reference station occupied by one receiver to determine coordinates of unknown points visited by a rover receiver [1]. Similar to static GPS the reference station is set on a point of known coordinates but the use of a data link, to transfer measurements acquired at the reference receiver to the roving receiver, permits the calculation of the rover coordinates at the time of measurement [2]. Reference [7] compares between total station and GPS tools from different points of view including range, accuracy, flexibility and price. He mentioned that the accuracy of total station is 3 to 10 times better than the GPS. Reference [11] compared RTK to static GPS and to total station and concluded that they reached an achievable and repeatable accuracy of approximately 2.5 cm. The measured points extend 1400 m away from the reference point
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