Applied Research Of GPS Leveling In Line-road Engineering Height Measurement

It's well known that the line-road engineering with the attribute of big survey area, long distance and complex terrain along surveying line. For a long time ,the elevation surveying in line-road engineering implemented by leveling methods for the advantage of its accuracy and feasibility, but the disadvantage such as high labour intensity and cost, lower efficiency etc limit the use of leveling at some circumstance.Global position system technology obtained the objects three dimension coordinate directly at any circumstance without the influence of weather and so on. It has become the importance measurement in line-road engineering. With the innovation and improvement of GPS technology, the GPS height precision improved at the same time. Currently, the GPS height information applied in small regional engineering projects was matured and the fitting methods broadly used. However, the abundant GPS height applied to several kilometers line-road engineering even hundreds kilometers of hilly and mountainous area was one of the hot topic in surveying fields.Firstly, this paper introduced the concept of geodetic height, orthometric height normal height and their relation one another. The theory about GPS height fitting and methods of quality control expatiated in detail such as isoline method, polynomial curve fitting, spline approximation method, moving average method, earth gravity model Neural Network methods an so on subsequently. Finally, based on VC++ platform and Matlab language, the abundant real GPS height data of Wuhan-Yichang Expressway and Wuhan No.1 Rail Transit Engineering was analyzed and compared by the developed program. Meanwhile, Some constructive advices and conclusions were given. GPS level points even design along the whole line-road, the space between level point and level point in plain areas is about 10 kilometers and the space between level point and level point in hill areas is about 4 kilometers. The results which are gained through the fitting with quadratic, thrice and quatic polynomial toroidal functions can meet the precision demands for third or fourth order class leveling.The results of research demonstrated that GPS height fitting equivalence to third or fourth order class leveling and can replaced the leveling in some condition to line-road engineering. The results have great benefit to vertical control surveying in line-road engineering.