GPS Elevation Fitting Used In Highway Engineering Survey

Global Positioning System provides three-dimensional coordinates include accurateposition of the plane and geodetic height of the observation points. While in china, normalhigh used as the national unified height system. Therefore, How to use the GPS measuredellipsoidal height to get the normal high which we need effectually to achieve the true senseof three-dimensional positioning has cause more attention and in-depth study.This article described the conception of the height fitter in detail. For example, geodeticheight, normal height, height anomaly, etc. And described the circumstances andcharacteristics of that GPS used in highway engineering and bridge and tunnel engineering indetails. Analyze the circumstances and characteristics of the problem of height transformation.At present, mathematical model fitting is often used. such as cubic spline fitting, polynomialcurve fitting, polynomial surface fitting and mobile surface fitting,etc. While there wareappeared new method of the height transportation, include neural network and gravitymeasurement.Commonly used method of fitting in engineering, such as polynomial curve fitting haslarger error of cut high fill low when used in highway engineering which has the large spanand complex terrain, because large vertical span would cause complex change of heightanomaly. While, cubic spline fit and mobile surface fit could suitable for this strip terrain.Especially it can solve the problem that overall fitting accuracy is low and segmentation pointdiscontinuous when piecewise fitting while the survey area is large. Among the two methods,cubic spline fitting have some drawbacks, cubic spline fitting will cause large errors whenhorizontal span is large. In this paper, with the engineering example has discussed the twomethods, by analyzing the result, we know that while horizontal span is small, terrain changesgently, the two methods can reach to accuracy of third-class standard. While the survey area islarge and terrain changes complex, cubic spline fitting would not applicable, while mobilesurface fitting can reach accuracy of substandard level. Meet the needs of different levels ofhighway projects, bridge and tunnel engineering.At last, use the language of Visual C++developed the system of height fit whichintegrated the methods of cubic spline fitting and mobile surface fitting. This greatly facilitates the fitting of GPS elevation.