In the framework of the GEODYnamics of South and South-East Asia (GEODYSSEA) project a network of 42 stations was observed by GPS during two field campaigns in 1994 and 1996. BKG and GFZ realized a third observation of the complete network in 1998. The data was analyzed independently by two analysis centers and a precision of the coordinate solutions was found to be 4-7 mm for the horizontal, and 10 mm for the vertical component. Subsequently, these campaign solutions were merged into one unique solution, which was accurately mapped into the International Terrestrial Reference Frame of 1997 (ITRF97). The global accuracy of this solution with respect to ITRF97 is of the order of 10 mm, while the resolution of the relative horizontal velocities is estimated to be at the level of 2-3 mm/yr. Comparison of the new solution with the previously published GEODYSSEA solution indicates, that improved results for the motion of Sundaland, South China and the overall deformation in the area could be found. Improvements are due to the increased time span and due to a better connection to and the advances in the ITRF reference frame. The new set of coordinates and velocities is used as the basis for scientific interpretations, which have been and will be published in separate papers.
The Peninsular Malaysia Geodetic Vertical Datum 2000 (PMGVD2000) inherited several deficiencies due to offsets between local datums used, levelling error propagations, land subsidence, sea level rise, and sea level slopes along the southern half of the Malacca Strait on the west coast and the South China Sea in the east coast of the Peninsular relative to the Port Klang (PTK) datum point. To cater for a more reliable elevation-based assessment of both sea level rise and coastal flooding exposure, a new epoch-based height reference system PMGVD2022 has been developed. We have undertaken the processing of more than 30 years of sea level data from twelve tide gauge (TG) stations along the Peninsular Malaysia coast for the determination of the relative mean sea level (RMSL) at epoch 2022.0 with their respective trends and incorporates the quantification of the local vertical land motion (VLM) impact. PMGVD2022 is based on a new gravimetric geoid (PMGeoid2022) fitted to the RMSL at PTK. The orthometric height is realised through the GNSS levelling concept H = hGNSS–Nfit_PTK–NRMDT, where NRMDT is a constant offset due to the relative mean dynamic ocean topography (RMDT) between the fitted geoid at PTK and the local MSL datums along the Peninsular Malaysia coast. PMGVD2022 will become a single height reference system with absolute accuracies of better than ±3 cm and ±10 cm across most of the land/coastal area and the continental shelf of Peninsular Malaysia, respectively.
The demand for positional accuracy and multi-dimensional data have demonstrated drastic changes in the geomatics data adjustment approach. Furthermore, the capability of modern sensors to provide high accuracy data (i.e., global navigation satellite system) has caused the crucial requirement for a rigorous adjustment that can process data from multi-sensors. Geomatics practitioners have gradually transformed the adjustment procedure to the most rigorous approach (i.e., parametric linear regression) to adapt to current demand. However, legacy datasets that utilize independent line constraint in the traditional adjustment approach have caused significant uncertainties in parametric linear regression (LR) adjustment. To resolve this dilemma, this research has designed robust experiments using closed traverse types: single-line constraint, multi-line constraints, and sub-network line constraint. Through errors trend and network form deterioration analyses, the outcomes have visually and numerically verified the insignificant of independent line constraints in parametric LR. However, the establishment of control points at the beginning or end of lines could solve the limitation of the abovementioned issue. In both analyses, control points at initial lines have demonstrated the best solution for constrained adjustment. The obtained results have exemplified the appropriate implementation of network adjustment in the presence of line constraints. As positional accuracy becomes the main priority, it can be concluded that points-based constraints are more advisable in preserving the quality of cadastral network adjustment.
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