Datum cad 2018
In 1983, the NAD27 datum was eventually replaced with NAD83. 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. Any point with a latitude and longitude away from this reference point could be measured 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. Kansas was selected 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. The North American Datum of 1927 (NAD27) is one of the main three geodetic datums used in North America. All coordinates on Earth are referenced to a horizontal datum. Geodetic datums form the basis of coordinates of all horizontal positions on Earth. Geodesists use a horizontal datum as the model to translate a spheroid/ellipsoid into locations on Earth with latitude and longitude lines. Most historical USGS topographic maps and projects by the US Army Corps of Engineers used NAD27 as a reference system.Ī horizontal datum provides a frame of reference as a basis for placing specific locations at specific points on the spheroid. Overall, it established a network of standardized horizontal positions in North America. NAD27 is the adjustment of long-baseline surveys. NAD27 stands for the North American Datum of 1927.