Research On Geoid Surface Fitting Based On EGM2008 Model And Multi-face Function

Correction of EGM2008 model,improvement of multi-face function model,the core point of multi-surface function fitting and selection of smoothing factor are discussed in order to study those.Hong Kong geodetic refinement data are used to correlate the related test.Finally,the 2'×2' geoid grid model in Hong Kong is established.The results show that the errors of the unit weight of the Hong Kong geoid by the multi-face function model with intercept,the multi-face function model without intercept,the cubic surface model and the “remove-restore” method are ±1.15 cm,±1.29 cm and ± 2.23 cm respectively.The external coincidence test errors obtained by usage of the check point are±2.11 cm,±2.09 cm,and ±1.92 cm respectively.The main conclusions of this study are as follows:(1)The method of fitting the geoid based on the EGM2008 model and the multi-faceted function is feasible,which can effectively improve the accuracy of the fitting.The accuracy of the fitting is improved about 1 cm compared with the cubic surface fitting when using the multi-faceted function to perform that.(2)The improved multi-faceted function model,the core point and smoothing factor selection method in the multi-faceted function fitting proposed in this paper have played a very good role in improving the function practicability and the fitting accuracy.The accuracy of the multi-faceted function with intercept is the highest,the multi-faceted function without intercept is the second,and the cubic surface fitting is the worst.As far as the external coincidence test is concerned,the results obtained are just the opposite,but they are generally the same.Considering that the number of points participating in the external coincidence test is 25,the number of samples is a non-large sample(more than30),and the calculation method of the external coincidence accuracy is still to be discussed.Therefore it is determined that there is an intercept when performing the geoid fitting.The multi-faceted function model is the best.(3)The grid level Hong Kong geoid model obtained in the study can be directly used for GNSS level measurement,and the model has practicality and research value.