Geodesy from ASTROLABE to GPS-A Navigator's View

Since the 17th century, it has been known that the earth's shape is approximately elliposidal. Spherical approximations of the earth's shape, with the exception of meridional parts (meridian distances), were accurate enough for most navigation until the early 1960s. With the advent of a satellite-based Global Positioning System (GPS), navigational accuracy improved to the point where Geodesy, the science concerned with the size and shape of the earth, became very important. This paper addresses the history of geodetic observation or surveying, discusses the size and shape of the earth and the refinements resulting from greater precision of measurement, and describes world geodetic systems compared to older datums. Application of the many facets of Geodesy to navigation, such as the significance of geoidal height and mean sea level, and transformation from WGS-72 to local datums, are also discussed.