Evaluating the range of differences between GPS rapic-static observed orthometric height with the digital precise levelling

摘要

An elevation is a vertical distance above or below a references datum. In surveying, the references datum that is universally employed is that of mean sea level (MSL). GPS observation give a reasonable accuracy of height for construction work but how much different the value of height the current GPS technology can be achieve if compare to the precise levelling technique. The aim of this study is to compare the corrected GPS height with a looped precise levelling applied with least square adjustment. Prior to performing any of surveying work, the instrument must be calibrated. Two type of calibration were carried out. First is two peg test and second calibration is GPS Baseline Test. This study was conducted in the vicinity of University Technology Mara in Shah Alam, Selangor. Height observations were recorded at temporary and permanent monuments using digital precise levelling and rapid static GPS. Heights at permanent monuments with published elevations were observed using each method and served as control and to check the quality of all measurements. The precise levelling starts at the Benchmark and passing through all the established Temporary Bench Mark (TBM) until the second Benchmark and the close back at the starting points. Then, from the starting point closed again to the second benchmark to make are two loops. For the GPS observation, one hour static observation was conducted on selected common station. The data observation processed using the Transfer, Reduction, and Adjustment Electronic Level Program for Electronic Digital Level and Topcon Tool software for GPS instrument. The data from the Electronic Digital Level observation will be applied with the least square adjustment. The result both instruments are compared to get the different of from GPS Static observation.