Accuracy Assessment an Improvement for Level Survey Survey using Real Time Kinematic (RTK) GPS
Dinesh Manandhar1, kiyoshi Honda1, Shunji Murai1,Sachio Kubo2, Masahiro Yonemura2
1space Technology Application and Research
Asian Institute of Technology
P.O. Box 4, Klong Luang, Pathumathani 12120, Thailand
E-mail : Dinesh_nep@hotmail.com, honda@ait.ac.th
2Keio University, Japan
Abstract
The global Positioning System (GPS) is a satellite based positioning and navigation system that provides precise position, velocity and time information. The height accuracy is GPS is lower than the planimetric accuracy. The paper discusses about the height accuracy achievable in real time kinematics mode using single frequency GPS wit Ovatel's RT20 algorithm. Analysis was also done to see whether there is any correlation between the antenna velocity (speed ) and the accuracy. As a core part of the reach, a procedural was developed to improve the height accuracy based on the observed data in RTK mode. This was accomplished by using two calibration points as reference and distributing the errors among the observed points. This improved the accuracy to a few centimeters level (2-4cm, RMS), which is a very significant improvement.
Introduction
The successful application of GPS is dependent on understanding its coordinate system, achievable accuracy and limitations. All GPS modes of operation are to the same. Accuracy ranging from hundred meters to a few millimeters cab be achieved depending upon the data collection and processing techniques, hardware, software, satellite geometry and atmospheric condition.
In order to optimize the survey time, it is necessary to know there accuracy achievable in different modes of operation. It is also necessary to know the procedures in order to achieve higher accuracy. A GPS cab be used for level survey provided that the accuracy achievable is good enough for the desired application. In their research a procedural was developed to achieve centimeter level accuracy in height component, which could be useful for level suvey.
Objective
The main objective of this research is to improve the height accuracy observed in real time kinematics (RTK) mode.
Research Structure
The structure of this research is shown in figure 1. the structure mainly consists of four components. The first one is to develop the system itself, sine this is the first time a base station was installed in Thailand ( and hence at AIT) using mobile phone for real time differential correction. The next component includes the accuracy analysis in both the static and kinematic modes. In static mode, the accuracy was analyzed for plan metric and height accuracy was analysed. The height accuracy achieved in kinematic mode was compared with the level survey. An overhead road crossing at a base length of three kilometer was chosen for real time kinematic survey. The road is about 750 meters long, elevated up to eight meters ( approximately) at the center of the road and has 31 piers. The error at each pier location was calculated and analysed to see whether there was any effect of antenna velocity ( vehicle speed) on accuracy. Next , the analysis was done to see whether the errors could be minimized. The RMS error, the standard deviation of the error itself and the scatter plot between the errors at the calibration points were analysed. Based on these analysis and the two calibration points an error correction technique was applied to distribute the errors among the observed points
