This is the mathematical model for the shape of the earth used on whatever map you're reading. The more recent ones are global, but many regional and local datums are in use as well. These may have values that fit the shape of the earth well over a continent, but perform less well when applied to the whole earth. Generally the datum is named somewhere on the margins of the map.
|Select Datum From Drop-Down List:|
|Equatorial Radius (meters):||Polar Radius (meters):|
Cross Check: As soon as you perform a conversion in one mode, the results are immediately entered as input into the others. For example, if you convert 44.5 N 88.5 W to UTM, you get Easting 380749.6, Northing 4928286.8. These values appear in the output boxes, but they also appear in the input boxes for converting UTM to geographic coordinates. You can then click the conversion button and compare the geographic coordinates with your original input. Note: a discrepancy of .001 seconds equals about 3 cm.
Out-of-Zone Calculations: Sometimes you have adjacent points that straddle a zone boundary, and they will have wildly different UTM coordinates even though they are very close together on the ground. For example, 45 N 89.9 W and 45 N 90.1 W are only about 15 km apart on the ground, but their UTM easting coordinates are 271428.8E and 728571.2 E. Even though it's not technically correct, it's sometimes a lot more useful to extend the grid across the zone boundary. For the UTM to Latitude-Longitude conversion, simply enter the coordinates and the desired zone. For example, Zone 15 extends from 90 to 96 W, but if you enter easting 750000, northing 5000000, zone 15, you'll get latitude 45.111N, longitude 89.82W, that is, a longitude in Zone 16.
If you calculate coordinates across normal zone boundaries, alert messages may appear warning you that the results may be unreliable. Unless you specifically intend to carry grids across zone boundaries, you should consider these error messages and correct your input.
Latitude (Degrees): Longitude (Degrees):
Degrees, Minutes, Seconds
Latitude Degrees: Minutes: Seconds:
Longitude Degrees: Minutes: Seconds:
Easting: Northing: Zone: South of Equator:
NATO UTM (meters)
Because digraphs repeat every 2000 km in the north-south direction, and every three zones east-west, a full zone description is necessary for an unambiguous conversion.
Created 29 November 2010, Last Update 21 March 2014
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