Alternative of Terrestrial Data Processing for Precise Point Positioning

Abstract

Terrestrial mapping is performed on the topographic surface, but control points are typically defined using a Projected Coordinate System (PCS). Using PCS directly as control points in terrestrial data processing can cause problems in final result. They must be corrected before, due to the discrepancies between the projection plane and the ellipsoid, and between the ellipsoid and the topographic surface. To address this, we propose an alternative approach that involves defining a custom ellipsoid that intersect with the topographic surface. In practice, this approach utilizes a control point whose coordinate is defined using PCS on the custom ellipsoid. To test this concept, we conducted a calculation of an open traverse survey spanning 10 km east-west and measuring an elevation of 1000 m above the reference ellipsoid. The traverse survey included two control points at the beginning and end, and two check points every 3 km. The traverse calculation was done using four different coordinate systems, including a combination of WGS84 and custom ellipsoid for the datums, and Universal Transverse Mercator zone 48 south (UTM48S) and Transverse Mercator (TM) with custom central meridian for the projections. After the calculation, we found that the lowest linear misclosure value was produced by the combination of custom datum-custom TM. The coordinate at the check point was then evaluated and the result showed that the total linear misclosure of the combination of custom datum-custom TM was not significantly different from WGS84-custom TM, with values of only differ by less than 1mm.While the difference of linear misclosure with standard data processing differ by 8 mm. Based on this result, we can conclude that the use of proper projection system in control point coordinate definition or combine with custom datum is the best option for open traverse without control at the end.