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An MGRS grid reference is a point reference system. When the term 'grid square' is used, it can refer to a square with a side length of 10 km (6 mi), 1 km, 100 m (328 ft), 10 m or 1 m, depending on the precision of the coordinates provided.
In geodesy, conversion among different geographic coordinate systems is made necessary by the different geographic coordinate systems in use across the world and over time. Coordinate conversion is composed of a number of different types of conversion: format change of geographic coordinates, conversion of coordinate systems, or transformation ...
Times relative to the designation are indicated with +/−[Arabic numeral] after the letter, replacing -day or -hour with a count of the same unit: "D−1" (the day before D-Day), "L+9" (9 hours after L-Hour) etc. [citation needed] In less formal contexts, the symbol or numeral may be spelled out: "D minus 1" or "L plus nine." [citation needed ...
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If the reference direction is north (either true north, magnetic north, or grid north), the bearing is termed an absolute bearing. In a contemporary land navigation context, true, magnetic, and grid bearings are always measured in this way, with true north, magnetic north, or grid north being 0° in a 360-degree system. [5]
Longitude, being up to 180° east or west of a prime meridian, is mathematically related to time differences up to 12 hours by a factor of 15. Thus, a time differential (in hours) between two points is multiplied by 15 to obtain a longitudinal difference (in degrees). Historically, times used for calculating longitude have included apparent ...
Recent editions of these maps (those referenced to the North American datum of 1983, or NAD83) are compatible with USNG, and current editions also contain a standard USNG information box in the collar which identifies the GZD(s) (Grid Zone Designator(s) and the 100 km Grid Square ID(s) covering the area of the particular map. USNG can now be ...
The reverse conversion is harder: given X-Y-Z can immediately get longitude, but no closed formula for latitude and height exists. See "Geodetic system." Using Bowring's formula in 1976 Survey Review the first iteration gives latitude correct within 10-11 degree as long as the point is within 10,000 meters above or 5,000 meters below the ellipsoid.