Abstract:
The measurement of geoid in Thailand has recently gained its importance. Applications of geoid model can be used to determine the orthometric heights of geoid surface from relative reference GPS ellipsoid. The main objective of this research is to develop a local geoid model in central part of Thailand using the interpolation method. A total of 70 GPS points positioning were used for this observation. The GPS signals and the first order leveling survey marks measurement were provided by the Royal Thai Survey Department (RTSD). These data were then used to generate a local geoid model in the central region of Thailand. Subsequently, this local geoid model was assessed by 20 check points within the research area. This research revealed an average error values of the orthometric heights of geoid surface from 4 different interpolation methods which are 1) Inverse Distance Weighted (IDW), 2) Kriging, 3) Spline and 4) Triangulated Irregular Network (TIN). IDW method gave an average error value at 1.6 centimeter with the largest discrepancy at 15.7 centimeter. While Kriging, Spline and TIN gave 1.7 centimeter with the largest discrepancy at 5.2 centimeter, 1.3 centimeter with the largest discrepancy at 5.4 centimeter and 1.4 centimeter with the largest discrepancy at 5.4 centimeter, respectively. In conclusion, the results confirm that the Kriging, Spline and TIN methods can be accurately used to evaluate the orthometric heights from relative reference GPS ellipsoid within the central region of Thailand.