On Estimating Map Model Errors and GPS Position Errors (Applying More Science to the Art of Navigation)

Peter Kielland, Tony Tubman

Abstract: In order to decide whether a desired maneuver can or can’t be safely undertaken, a prudent navigator must be aware of both the current spatial uncertainty of his vehicle’s positioning system and the spatial uncertainty of the navigational map model being used to depict the theater of operations. From this safety to navigation perspective, knowledge of data accuracy is as important as the data itself. This paper discusses the Electronic Chart (EC) implications of both GPS vehicle positioning errors and the relatively large data modeling errors specific to bathymetric map models (charts). It proposes and demonstrates software solutions which statistically evaluate both of these spatial uncertainties and graphically integrates the two stochastic models within an EC environment. The paper also documents an experiment carried out by the Canadian Hydrographic Service, designed to insure that real-time DGPS users compute statistically valid position error estimates. The experiment ground truthed the position error estimates obtained using a conventional real-time error analysis of pseudorange redundancy. Using this ground-truth information, an improved pseudorange error model was empirically determined. The new pseudorange error model is continually updated using the estimated pseudorange variances computed by the Novatel GPS receiver rather than applying the constant a priori pseudorange variance typical in least-squares adjustments. This dynamic range error model effectively reduced the statistical bias between the observed errors and their predicted error estimates. The improved range error model also significantly improved the performance of the position solution. All DGPS positions computed by the modified software had a positional accuracy of better than 0.5 meters.
Published in: Proceedings of the 1994 National Technical Meeting of The Institute of Navigation
January 24 - 26, 1994
Catamaran Resort Hotel
San Diego, CA
Pages: 869 - 881
Cite this article: Kielland, Peter, Tubman, Tony, "On Estimating Map Model Errors and GPS Position Errors (Applying More Science to the Art of Navigation)," Proceedings of the 1994 National Technical Meeting of The Institute of Navigation, San Diego, CA, January 1994, pp. 869-881.
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