Virtual Differential GPS & Road Reduction Filtering by Map Matching

George Taylor, Geoffrey Blewitt

Abstract:	A novel method of map matching using the Global Posi-tioning System (GPS) has been developed for civilian use, which uses digital mapping data to infer the <100 meters systematic position errors which result largely from “se-lective availability” (S/A) imposed by the U.S. military. A method of rapidly detecting inappropriate road centre-lines from the set of all possible road centre-lines that a vehicle may be travelling on has been developed. This is called the Road Reduction Filter. The S/A error vector is estimated in a formal least squares procedure as the vehi-cle is moving. This estimate can be thought of as a posi-tion correction from a “virtual” differential GPS (DGPS) base station, thus providing an autonomous alternative to DGPS for in-car navigation and fleet management. We derive a formula for “Mapped Dilution of Precision” (MDOP), defined as the theoretical ratio of position preci-sion using virtual DGPS corrections to that using perfect DGPS corrections. This is shown to be purely a function of route geometry, and is computed for examples of basic road shapes. MDOP is favorable unless the route has less than a few degrees curvature for several kilometers. MDOP can thus provides an objective estimate of posi-tioning precision to a vehicle driver. Precision estimates using MDOP are shown to agree well with “true” posi-tioning errors determined using high precision (cm) GPS carrier phase techniques.
Published in:	Proceedings of the 12th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1999) September 14 - 17, 1999 Nashville, TN
Pages:	1675 - 1684
Cite this article:	Taylor, George, Blewitt, Geoffrey, "Virtual Differential GPS & Road Reduction Filtering by Map Matching," Proceedings of the 12th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1999), Nashville, TN, September 1999, pp. 1675-1684.
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