High-Precision Application of GPS in the Field of Real-Time Equipment Positioning

In the frame of its research about real-time positioning and control of road construction equipment, the « Laboratoire Central des Ponts et Chaussees, has carried out in 1996 a study to know more about the actual vertical accuracy that a RTK1 GPS2 could reach under worksite conditions. This study has widely used the dedicated testing facility SESSYL, built to perform high-accuracy and real- time evaluation tests on positioning systems. It has been performed in collaboration with the French road contractor COLAS and the « Ecole Superieure des Geometres et Topographes » (ESGT). First, is proposed an adapted geodetic transformation procedure, compatible with the high accuracy of the requirements. Then are presented the main results of a special SESSYL tests program, where the impacts of several influencing parameters on the vertical accuracy have been carefully examined. The core part of the paper is the analysis of the typical RTK GPS set of data, from which we have tried to extract two different components: a high-frequency noise, rather easy to filter, and a low-frequency bias. This bias, given its good repeatability, can be modeled and used in prediction to improve in real-time the raw accuracy of the data. As a full scale validation of our study, is finally described a site experiment, carried out this time on a real piece of equipment (an asphalt paver) during a real work site.1RTK: Real Time Kinematic 2GPS Global Positioning System