Where in the World Are We?

J. F. Roeber

Abstract: The coordinate converter-equipped radionavigation receiver is now commonplace. Is its ease of use an unmitigated blessing? Most U.S. civil charts are printed using North American Datum - 1927, while coordinate converters are based on World Geodetic System - 1972. The variations between these two common descriptions of the shape of the Earth range from zero to nearly 200 meters in U.S. waters. It is fortunate that the majority of precise navigation in the U.S. is performed utilizing systems (usually Loran-C) in their repeatable mode. Those systems employed in an "absolute" accuracy sense are generally not accurate enough to be affected by problems with coordinate conversion (although differences between WGS-72 and local chart datums can be as much as 1/2 km). The presence and growth of the Global Positioning System, a system with civil accuracies of 15 to 30 meters, will reveal the coordinate conversion problems here-to-fore disguised by use of less accurate systems. Military and numerous foreign charts, have offered, for some years, published corrections from WGS-72 to the chart datum. This far from ideal solution requires mental arithmetic, or entry of corrections into the coordinate converter before positions can be plotted. It is still better than the situation on the vast majority of charts available to the civil mariner which carry no means of effecting corrections. National Ocean Service has proposed a p 1 an which will convert, over a five-year period, most of their large-scale charts to NAD-1983, a description of the Earth which closely approximates WGS-84 soon to be the basis for GPS positions. The marine electronics manufacturer, and ultimately the mariner, is thus faced for the next 5 - 10 years with an "alphabet soup" of conflicting chart and coordinate converter datum/ellipsoid combinations. With no brilliant solution to offer, this paper relies on "education of the consumer" as the only way out of this multi-variable problem.
Published in: Proceedings of the 42nd Annual Meeting of The Institute of Navigation (1986)
June 24 - 26, 1986
Seattle, Washington
Pages: 120 - 121
Cite this article: Roeber, J. F., "Where in the World Are We?," Proceedings of the 42nd Annual Meeting of The Institute of Navigation (1986), Seattle, Washington, June 1986, pp. 120-121.
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