Coordinate transformation between two geodetic datums of Taiwan by least-squares collocation

Recently, the new Taiwan geodetic datum 1997 (TWD97) based on the Global Positioning System measurements has been established. Compared to the old geodetic datum, namely the Hu-Tzi-Shan datum, the TWD97 datum is more precisely defined. Since the TWD97 datum is a three-dimensional geocentric datum, while the Hu-Tzi-Shan datum is a locally defined horizontal datum and its triangulation points are deficient in the precise ellipsoidal height information, a three-dimensional coordinate transformation between both datums is therefore not appropriate. Moreover, there are the perceptible systematic errors in the triangulation networks in the Hu-Tzi-Shan datum. It is difficult to handle the systematic errors by ordinary datum transformation methods. In the paper, the technique of least-squares collocation is applied to the two-dimensional transformation from the Hu-Tzi-Shan datum to the TWD97 datum. By the present method, the systematic errors are predicted, and the coordinates of common points of both datums can be unchanged after the transformation. Our results show that the better transformation accuracy can be achieved by the least-squares collocation.