Surveyors and geodesists created a global ellipsoid model because of the enhancement of computing capabilities and GPS technology. The radio waves transmitted by GPS satellites enable extremely precise Earth measurements across continents and oceans. It wasn’t until the mainstream use of Global Positioning Systems (GPS) that we developed a unified global ellipsoid model. WGS84: Unifying a Global Ellipsoid Model with GPS In 1983, surveyors eventually replaced the NAD27 with NAD83.ģ. This set of horizontal positions formed the basis for the North American Datum of 1983 (NAD83). For example, surveyors benchmarked approximately 250,000 stations. NOAA’s National Geodetic Survey used these survey stations and triangulation to form the NAD27 datum.Īs time went on, the number of stations also grew.
At each station, surveyors collected latitudes and longitude coordinates.
Surveyors gathered approximately 26,000 stations in the United States and Canada. Surveyors could measure any point with a latitude and longitude away from this reference point based on the Clarke Ellipsoid of 1866. The latitudes and longitudes of every other point in North America were based on its direction, angle, and distance away from Meade’s Ranch. Surveyors chose Kansas as a common reference point because it was near the center of the contiguous United States.
This datum uses the Clarke Ellipsoid of 1866 with a fixed latitude and longitude at Meade’s Ranch, Kansas. NAD27 uses all horizontal geodetic surveys collected at this time using a least-square adjustment.
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