Datum
it defines the relationship between a local and a global three dimensional coordinate system of the same type, and it is defined as a re-position of a reference ellipsoid to be more accurate in representing a specific area . it also called local datum or national datum or just a datum. Because an ellipsoid may be a best fit globally and the difference between the geoid and ellipsoid (n) be very minimum (globally) but not necessary for a specific area (country for example) so that a datum is created. As every country wish to have an ellipsoid that is much accurate and close to the real surface of its land, some modifications may be applied to the previously best fitting global ellipsoid (correction for the ellipsoid parameters: a, b or e and f) or global reference system. Photo source And that by taking a point and consider it as a datum centre point (datum origin point, it’s fixed and all other points are calculated from it), by assuming that th...
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