UtmGridGenerator.GeodeticDatum Property
Gets or sets the GeodeticDatum used for the grid.
Syntax
public GeodeticDatum GeodeticDatum { get; set; }Property Value
Remarks
The UTM system was designed in the 1940s, before there was any useful global geodetic datum. So UTM has traditionally been used together with several local geodetic datums. If you use a local datum in a UtmGridGenerator, you should use a PolygonClipOperator to clip the grid to the region where the datum is used.
The two versions of MGRS can be motivated by the many geodetic datums. The new version of MGRS is not better than the old, it is just designed to be different. Given a complete MGRS position string (see Style), it is clear whether it was formed in the new or the old version, for the string can be valid in at most one of the versions (this is true everywhere except in latitude band X, between 72°N and 84°N, which is higher than the others). So, if someone uses a map with a UTM grid based on an old geodetic datum, we hope that the MGRS names on the map follow the old version of MGRS. Because if he receives an MGRS position string that is based on a new geodetic datum, using the new version of MGRS, then he will not be able to find the position on his map, so he will at least know that something is wrong.
To choose between old and new MGRS, you must find out whether NGA classifies your geodetic datum as old or new. Unfortunately, the various NGA documents - see UtmGridGenerator - do not agree on this topic. Reference 2 says that the old MGRS scheme is used for datums based on the ellipsoids Clarke 1866, Clarke 1880 and Bessel (presumably Bessel 1841). Reference 1 mentions the exception that the new MGRS scheme is used for the Luzon datum for the Philippines, despite that this datum is based on Clarke 1880. Reference 3, finally, says that the old MGRS scheme is used for all datums based on five ellipsoids: Clarke 1866, Clarke 1880, Clarke 1880 (IGN), Bessel 1841 and Bessel 1841 (Namibia), but for no other datums; the Luzon exception is not mentioned. See also the MgrsLetteringScheme enumeration, which is used by parsing and formatting utilities.
On a map of a European country, the UTM grid is probably in either WGS84 or ED50 (European Datum 1950, based on the International 1924 ellipsoid). National datums in Europe, like the Swedish RT90, are normally used only for the LongLat grid or for national projections.
Within USA there is also a civilian grid, United States National Grid (USNG), which is almost the same as MGRS: the grids agree for a modern datum like NAD83. For an old datum like NAD27, however, the MGRS would use the old MGRS scheme, whereas USNG would use the new MGRS scheme anyway, and specify the datum separately. See literature reference 3, listed at UtmGridGenerator.
Platforms
Windows, Linux, Android