Get the two letter 100k designator for a given UTM easting,
northing and zone number value.
@private
@param {number} easting
@param {number} northing
@param {number} zoneNumber
@return {string} the two letter 100k designator for the given UTM location.
Given the first letter from a two-letter MGRS 100k zone, and given the
MGRS table set for the zone number, figure out the easting value that
should be added to the other, secondary easting value.
Given the second letter from a two-letter MGRS 100k zone, and given the
MGRS table set for the zone number, figure out the northing value that
should be added to the other, secondary northing value. You have to
remember that Northings are determined from the equator, and the vertical
cycle of letters mean a 2000000 additional northing meters. This happens
approx. every 18 degrees of latitude. This method does NOT count any
additional northings. You have to figure out how many 2000000 meters need
to be added for the zone letter of the MGRS coordinate.
Converts UTM coords to lat/long, using the WGS84 ellipsoid. This is a convenience
class where the Zone can be specified as a single string eg."60N" which
is then broken down into the ZoneNumber and ZoneLetter.