I just wanted some simple conversions and transforms, and ended up with this. I must be a masachist.

Proj4JS has split out the MGRS handling to a separate module, possibly due to licensing issues. It is included in this library for the time-being, but has had a substantial refactor and rewrite from the original.

The main Mgrs classes have a mix of static methods that return new objects (Mgrs, LatLong, Square, Utm objects) and methods that operate on the current object. I intend to make it a little clearer which method does what. It has just inherited much of this from the JavaScript library, and partly from my learning curve in how the JavaScript library works.

namespace: Academe\Proj4Php\Mgrs

The LatLong and Square classes implement minimal interfaces to support the UTM and MGRS classes as a standalone module (nothing in Academe\Proj4Php\Mgrs depends on anything else). This may change, depending on whether Mgrs is split off into a separate library, or coupled more tightly with the other coordinate classes on the main Proj4Php library. It will probably depend on inherited licenses.

The LatLong class holds a latitude and longitude.

$latitude = 53.0;
$longitude = -5.5;

$lat_long = new LatLong($latitude, $longitude);
$lat_long = new LatLong(array($latitude, $longitude));

The Square class holds two LatLong classes to mark the opposite corners of the bounding box.

$square = new Square($lat_long_bottom_left, $lat_long_top_right);

The Utm class holds a UTM coordinate.

// From base UTM values.
$utm = new Utm($northing, $easting, $zone_number, $zone_letter);

// From latitude/longitude coordinates (WGS84 ellipsoid).
$utm = Utm::fromLatLong($latitude, $longitude);
$utm = Utm::fromLatLong($lat_long);

// Back to lat/long.
$lat_long = $utm->toLatLong();

// To a UTM grid reference string.
$grid_reference = $utm->toGridReference(); // '39L 198447 8893330'
$grid_reference = (string)$utm;
$grid_reference = $utm->toGridReference('%z$l%EE%NN'); // '39L0198447E8893330N'

The UTM grid reference formatting fields are:

• %z Zone number
• %l Zone letter
• %h Hemisphere letter (N or S)
• %e Easting
• %n Northing
• %E Easting left-padded to 7 digits
• %N Northing left-padded to 7 digits

The Mgrs class extends Utm with its set of reference conversion methods.

// Create from base UTM values.
$mgrs = new Mgrs($northing, $easting, $zone_number, $zone_letter);

// From lat/long (same as for Utm)
$mgrs = Mgrs::fromLatLong($latitude, $longitude);
$mgrs = Mgrs::fromLatLong($lat_long);

// From a MGRS grid reference.
// The accuracy of the reference is noted and stored with the reference.
$mgrs = Mgrs::fromGridReference($mgrs_grid_reference);

// To a MGRS grid reference string.
// Template is optional, defaulting to '%z%l%k%e%n'.
// The accuracy is optional 0 to 5, defaulting to 5.
$grid_reference = $mgrs->toGridReference($template, $accuracy);

// To a single lat/long coordinate in the *centre* of the square according to
// teh accuracy, to one metre.
// $accuracy is optional, and defaults to the accuracy of the current coordinate.
$lat_long = $mgrs->toPoint($accuracy);

// The bottom left coordinate, disregarding the accuracy (like toPoint with the
// maximum accuracy of 5).
$lat_long = $mgrs->toLatLong();

// To a Square region.
// The accuracy is optional 0 to 5, defaulting to 5.
$square = $mgrs->toSquare($accuracy);

The MGRS grid reference formatting fields are:

• %z Zone number
• %l Zone letter
• %k 100km zone ID (two letters)
• %e Easting, to the current accuracy
• %n Northing, to the current accuracy

Instantiating a Utm, Mgrs, LatLong or Square class always requires a valid coordiate in some form.

• http://www.luomus.fi/en/utm-mgrs-atlas-florae-europaeae
  Description of the UTM/MGRS grid systems
• http://www.earthpoint.us/convert.aspx
  Good converter site for testing against
• http://en.wikipedia.org/wiki/Military_grid_reference_system
  MGRS grid reference format definition and examples.
• http://therucksack.tripod.com/MiBSAR/LandNav/UTM/UTM.htm
  Great description of how the UTM grid reference works, including the polar regions. Has an emphasis on how the system is used my map readers and users.