Centimeter‐Level Relative Positioning with GPS

Abstract

Although the Global Positioning System (GPS) was designed primarily for real‐time navigation and positioning applications at the dekameter (10‐m, or 33‐ft) level of accuracy, the GPS has been used to determine the relative position coordinates of fixed points with centimeter‐level accuracy, when the distance between the points has been of the order of 10 km. All three position coordinates are determined with this accuracy. For inter‐site distances less than 1 km the uncertainty is about 3 mm, and for distances greater than 10 km the uncertainty in each coordinate is about 1–2 parts per million (ppm) of the distance. These results have been obtained with commercially available production equipment (MACROMETER model V‐1000 Interferometric Surveyors) operated by regular surveying personnel under real field conditions, not just by university scientists under ideal laboratory conditions. However, at MIT techniques that promise to reduce the uncertainty to 1 part in 107 for distances greater than 10 km are being developed.