A study on time-variant datum application for cadastral surveying in the Taiwan Area

With the advent of space geodesy techniques, the absolute position of control points is revealed to change with time. This leads to the issues of time-variant datum. Taiwan is located in the margin of the deforming area; the velocity field is varied and complex. The long-term deforming trend and the patch cause the variations of displacement and the local relative deformation. This phenomenon also affects the control and the cadastral surveying, in which the regulations of relative accuracies are adopted. In this study, several aspects of surveying tasks are examined and the results reveal that the dynamic corrections are imperatively needed in the application of the static datum. However, the issue of the variation in land area should be faced if the time-variant datum is adopted. The results in this study show that the variation in land area due to the long-term deforming trend is slight and much smaller than that caused by the survey errors. In order to ease the impact of adopting time-variant datum to the society, regulations and legal procedures should be established first to accommodate the potential change of registered land area.