Site Calibration of GPS Grid Coordinates for Implementation of Machine Guidance System

The positioning of machine is the essential part for the success of machine guidance. The measuring of positions can be easily made using Global Positioning System (GPS). However, a conversion of the positions measured using GPS to those given in a design sheet is indispensable. Thus, site-specific parameters should be calculated for successful application to machine guidance. The tuning of site-specific conversion parameters is called a site calibration. In this study two types of conversion methods, so called seven-parameter and four-parameter methods, are employed to convert the GPS-measured positions into the local grid positions. The conversion parameters are tuned to get site-specific values for a given construction site by matching the GPS-measured positions and the local grid positions at the site. The site-specific parameters are validated by comparing the grid coordinates converted from the GPS-measured positions and the grid coordinates measured using a total station. Both the seven-parameter and the four-parameter methods give the maximum root-mean-square error of 0.0423m for the control points along the site boundary. On the other hand, for the interior points which are not used in the calibration the four-parameter method gives the maximum rms error of 0.026m which is slightly better than that given by the seven-parameter method. All the rms errors fall below 0.05m which is small enough for the use for the machine guidance in the construction site. From the validity test it is concluded that both the seven-parameters and the four-parameters are appropriate for the construction site. Compared to the four-parameter method, the calibration using seven-parameter method involves more complex process. Also, the seven-parameter calibration requires additional information on the elevation, the local ellipsoid, and the projection type. The disadvantage of four-parameter calibration is the coverage limit of 10 km square. However, there are only a few construction sites in Korea that are bigger than 10 km square. Given that both seven-parameter and four-parameter calibrations are appropriate, using much simpler four-parameter calibration can be more efficient.Maste