EFFECTS OF LARGE VERTICAL DEFLECTIONS IN A HIGH PRECISION NETWORK

The purpose of this study is to investigate the effects of very large vertical deflections in a high precision network. The paper focuses on those effects of the vertical deflections which are often ignored or mistreated and errors owing to the use of approximate reductions and predicted astrogeodetic vertical deflections at stations. Part of the Taiwan Geodetic Datum of 1980 (TGD80) first order triangulation network has been the source of the data used to investigate the effects. With the proper reduction equations, all terrestrial observations were first adjusted with a GPS determined geodetic baseline and azimuth in a combination adjustment (Group 1), and then all directions, distances and astronomic azimuths were adjusted together without GPS information (Group 2). The results obtained in this study show that the astronomic station which had the largest vertical deflections in TGD80, creates a maximum position error of 14.2 cm when the rigorous Laplace equation was replaced by the simplified Laplace equation in the Group 1 case.