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| | Datum and Earth Ellipsoid -- 3DSoftware.com (Site not responding. Last check: 2007-10-21) |
 | | The choice of the reference ellipsoid used for various regions of the Earth has been influenced by the local geoid, but large-scale map projections are designed to fit the reference ellipsoid, not the geoid. |
 | | The Bessel ellipsoid of 1841 was used by the Coast Survey from 1844 until 1880, when the bureau adopted the 1866 evaluation by the British geodesist Alexander Ross Clarke using measurements of meridian arcs in western Europe, Russia, India, South Africa, and Peru. |
 | | The polar axis of the reference ellipsoid for such a region, therefore, normally does not coincide with the axis of the actual Earth, although it is assumed to be parallel. |
| www.3dsoftware.com /Cartography/USGS/MapProjections/DatumEllipsoid (1883 words) |
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