@vizlabdev/geodesy
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Libraries of geodesy functions
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JavaScript
/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
/* MGRS / UTM Conversion Functions (c) Chris Veness 2014-2019 */
/* MIT Licence */
/* www.movable-type.co.uk/scripts/latlong-utm-mgrs.html */
/* www.movable-type.co.uk/scripts/geodesy-library.html#mgrs */
/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
import Utm, { LatLon as LatLonEllipsoidal, Dms } from './utm.js';
/**
* Military Grid Reference System (MGRS/NATO) grid references provides geocoordinate references
* covering the entire globe, based on UTM projections.
*
* MGRS references comprise a grid zone designator, a 100km square identification, and an easting
* and northing (in metres); e.g. ‘31U DQ 48251 11932’.
*
* Depending on requirements, some parts of the reference may be omitted (implied), and
* eastings/northings may be given to varying resolution.
*
* qv www.fgdc.gov/standards/projects/FGDC-standards-projects/usng/fgdc_std_011_2001_usng.pdf
*
* @module mgrs
*/
/*
* Latitude bands C..X 8° each, covering 80°S to 84°N
*/
const latBands = 'CDEFGHJKLMNPQRSTUVWXX'; // X is repeated for 80-84°N
/*
* 100km grid square column (‘e’) letters repeat every third zone
*/
const e100kLetters = [ 'ABCDEFGH', 'JKLMNPQR', 'STUVWXYZ' ];
/*
* 100km grid square row (‘n’) letters repeat every other zone
*/
const n100kLetters = [ 'ABCDEFGHJKLMNPQRSTUV', 'FGHJKLMNPQRSTUVABCDE' ];
/* Mgrs - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
/**
* Military Grid Reference System (MGRS/NATO) grid references, with methods to parse references, and
* to convert to UTM coordinates.
*/
class Mgrs {
/**
* Creates an Mgrs grid reference object.
*
* @param {number} zone - 6° longitudinal zone (1..60 covering 180°W..180°E).
* @param {string} band - 8° latitudinal band (C..X covering 80°S..84°N).
* @param {string} e100k - First letter (E) of 100km grid square.
* @param {string} n100k - Second letter (N) of 100km grid square.
* @param {number} easting - Easting in metres within 100km grid square.
* @param {number} northing - Northing in metres within 100km grid square.
* @param {LatLon.datums} [datum=WGS84] - Datum UTM coordinate is based on.
* @throws {RangeError} Invalid MGRS grid reference.
*
* @example
* import Mgrs from '/js/geodesy/mgrs.js';
* const mgrsRef = new Mgrs(31, 'U', 'D', 'Q', 48251, 11932); // 31U DQ 48251 11932
*/
constructor(zone, band, e100k, n100k, easting, northing, datum=LatLonEllipsoidal.datums.WGS84) {
if (!(1<=zone && zone<=60)) throw new RangeError(`invalid MGRS zone ‘${zone}’`);
if (zone != parseInt(zone)) throw new RangeError(`invalid MGRS zone ‘${zone}’`);
const errors = []; // check & report all other possible errors rather than reporting one-by-one
if (band.length!=1 || latBands.indexOf(band) == -1) errors.push(`invalid MGRS band ‘${band}’`);
if (e100k.length!=1 || e100kLetters[(zone-1)%3].indexOf(e100k) == -1) errors.push(`invalid MGRS 100km grid square column ‘${e100k}’ for zone ${zone}`);
if (n100k.length!=1 || n100kLetters[0].indexOf(n100k) == -1) errors.push(`invalid MGRS 100km grid square row ‘${n100k}’`);
if (isNaN(Number(easting))) errors.push(`invalid MGRS easting ‘${easting}’`);
if (isNaN(Number(northing))) errors.push(`invalid MGRS northing ‘${northing}’`);
if (!datum || datum.ellipsoid==undefined) errors.push(`unrecognised datum ‘${datum}’`);
if (errors.length > 0) throw new RangeError(errors.join(', '));
this.zone = Number(zone);
this.band = band;
this.e100k = e100k;
this.n100k = n100k;
this.easting = Number(easting);
this.northing = Number(northing);
this.datum = datum;
}
/**
* Converts MGRS grid reference to UTM coordinate.
*
* Grid references refer to squares rather than points (with the size of the square indicated
* by the precision of the reference); this conversion will return the UTM coordinate of the SW
* corner of the grid reference square.
*
* @returns {Utm} UTM coordinate of SW corner of this MGRS grid reference.
*
* @example
* const mgrsRef = Mgrs.parse('31U DQ 48251 11932');
* const utmCoord = mgrsRef.toUtm(); // 31 N 448251 5411932
*/
toUtm() {
const hemisphere = this.band>='N' ? 'N' : 'S';
// get easting specified by e100k (note +1 because eastings start at 166e3 due to 500km false origin)
const col = e100kLetters[(this.zone-1)%3].indexOf(this.e100k) + 1;
const e100kNum = col * 100e3; // e100k in metres
// get northing specified by n100k
const row = n100kLetters[(this.zone-1)%2].indexOf(this.n100k);
const n100kNum = row * 100e3; // n100k in metres
// get latitude of (bottom of) band
const latBand = (latBands.indexOf(this.band)-10)*8;
// get northing of bottom of band, extended to include entirety of bottom-most 100km square
const nBand = Math.floor(new LatLonEllipsoidal(latBand, 3).toUtm().northing/100e3)*100e3;
// 100km grid square row letters repeat every 2,000km north; add enough 2,000km blocks to
// get into required band
let n2M = 0; // northing of 2,000km block
while (n2M + n100kNum + this.northing < nBand) n2M += 2000e3;
return new Utm_Mgrs(this.zone, hemisphere, e100kNum+this.easting, n2M+n100kNum+this.northing, this.datum);
}
/**
* Parses string representation of MGRS grid reference.
*
* An MGRS grid reference comprises (space-separated)
* - grid zone designator (GZD)
* - 100km grid square letter-pair
* - easting
* - northing.
*
* @param {string} mgrsGridRef - String representation of MGRS grid reference.
* @returns {Mgrs} Mgrs grid reference object.
* @throws {Error} Invalid MGRS grid reference.
*
* @example
* const mgrsRef = Mgrs.parse('31U DQ 48251 11932');
* const mgrsRef = Mgrs.parse('31UDQ4825111932');
* // mgrsRef: { zone:31, band:'U', e100k:'D', n100k:'Q', easting:48251, northing:11932 }
*/
static parse(mgrsGridRef) {
if (!mgrsGridRef) throw new Error(`invalid MGRS grid reference ‘${mgrsGridRef}’`);
// check for military-style grid reference with no separators
if (!mgrsGridRef.trim().match(/\s/)) {
if (!Number(mgrsGridRef.slice(0, 2))) throw new Error(`invalid MGRS grid reference ‘${mgrsGridRef}’`);
let en = mgrsGridRef.trim().slice(5); // get easting/northing following zone/band/100ksq
en = en.slice(0, en.length/2)+' '+en.slice(-en.length/2); // separate easting/northing
mgrsGridRef = mgrsGridRef.slice(0, 3)+' '+mgrsGridRef.slice(3, 5)+' '+en; // insert spaces
}
// match separate elements (separated by whitespace)
const ref = mgrsGridRef.match(/\S+/g);
if (ref==null || ref.length!=4) throw new Error(`invalid MGRS grid reference ‘${mgrsGridRef}’`);
// split gzd into zone/band
const gzd = ref[0];
const zone = gzd.slice(0, 2);
const band = gzd.slice(2, 3);
// split 100km letter-pair into e/n
const en100k = ref[1];
const e100k = en100k.slice(0, 1);
const n100k = en100k.slice(1, 2);
let e = ref[2], n = ref[3];
// standardise to 10-digit refs - ie metres) (but only if < 10-digit refs, to allow decimals)
e = e.length>=5 ? e : (e+'00000').slice(0, 5);
n = n.length>=5 ? n : (n+'00000').slice(0, 5);
return new Mgrs(zone, band, e100k, n100k, e, n);
}
/**
* Returns a string representation of an MGRS grid reference.
*
* To distinguish from civilian UTM coordinate representations, no space is included within the
* zone/band grid zone designator.
*
* Components are separated by spaces: for a military-style unseparated string, use
* Mgrs.toString().replace(/ /g, '');
*
* Note that MGRS grid references get truncated, not rounded (unlike UTM coordinates); grid
* references indicate a bounding square, rather than a point, with the size of the square
* indicated by the precision - a precision of 10 indicates a 1-metre square, a precision of 4
* indicates a 1,000-metre square (hence 31U DQ 48 11 indicates a 1km square with SW corner at
* 31 N 448000 5411000, which would include the 1m square 31U DQ 48251 11932).
*
* @param {number} [digits=10] - Precision of returned grid reference (eg 4 = km, 10 = m).
* @returns {string} This grid reference in standard format.
* @throws {RangeError} Invalid precision.
*
* @example
* const mgrsStr = new Mgrs(31, 'U', 'D', 'Q', 48251, 11932).toString(); // 31U DQ 48251 11932
*/
toString(digits=10) {
if (![ 2, 4, 6, 8, 10 ].includes(Number(digits))) throw new RangeError(`invalid precision ‘${digits}’`);
const { zone, band, e100k, n100k, easting, northing } = this;
// truncate to required precision
const eRounded = Math.floor(easting/Math.pow(10, 5-digits/2));
const nRounded = Math.floor(northing/Math.pow(10, 5-digits/2));
// ensure leading zeros
const zPadded = zone.toString().padStart(2, '0');
const ePadded = eRounded.toString().padStart(digits/2, '0');
const nPadded = nRounded.toString().padStart(digits/2, '0');
return `${zPadded}${band} ${e100k}${n100k} ${ePadded} ${nPadded}`;
}
}
/* Utm_Mgrs - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
/**
* Extends Utm with method to convert UTM coordinate to MGRS reference.
*
* @extends Utm
*/
class Utm_Mgrs extends Utm {
/**
* Converts UTM coordinate to MGRS reference.
*
* @returns {Mgrs}
* @throws {TypeError} Invalid UTM coordinate.
*
* @example
* const utmCoord = new Utm(31, 'N', 448251, 5411932);
* const mgrsRef = utmCoord.toMgrs(); // 31U DQ 48251 11932
*/
toMgrs() {
// MGRS zone is same as UTM zone
const zone = this.zone;
// convert UTM to lat/long to get latitude to determine band
const latlong = this.toLatLon();
// grid zones are 8° tall, 0°N is 10th band
const band = latBands.charAt(Math.floor(latlong.lat/8+10)); // latitude band
// columns in zone 1 are A-H, zone 2 J-R, zone 3 S-Z, then repeating every 3rd zone
const col = Math.floor(this.easting / 100e3);
// (note -1 because eastings start at 166e3 due to 500km false origin)
const e100k = e100kLetters[(zone-1)%3].charAt(col-1);
// rows in even zones are A-V, in odd zones are F-E
const row = Math.floor(this.northing / 100e3) % 20;
const n100k = n100kLetters[(zone-1)%2].charAt(row);
// truncate easting/northing to within 100km grid square
let easting = this.easting % 100e3;
let northing = this.northing % 100e3;
// round to nm precision
easting = Number(easting.toFixed(6));
northing = Number(northing.toFixed(6));
return new Mgrs(zone, band, e100k, n100k, easting, northing);
}
}
/**
* Extends LatLonEllipsoidal adding toMgrs() method to the Utm object returned by LatLon.toUtm().
*
* @extends LatLonEllipsoidal
*/
class Latlon_Utm_Mgrs extends LatLonEllipsoidal {
/**
* Converts latitude/longitude to UTM coordinate.
*
* Shadow of LatLon.toUtm, returning Utm augmented with toMgrs() method.
*
* @param {number} [zoneOverride] - Use specified zone rather than zone within which point lies;
* note overriding the UTM zone has the potential to result in negative eastings, and
* perverse results within Norway/Svalbard exceptions (this is unlikely to be relevant
* for MGRS, but is needed as Mgrs passes through the Utm class).
* @returns {Utm} UTM coordinate.
* @throws {Error} If point not valid, if point outside latitude range.
*
* @example
* const latlong = new LatLon(48.8582, 2.2945);
* const utmCoord = latlong.toUtm(); // 31 N 448252 5411933
*/
toUtm(zoneOverride=undefined) {
const utm = super.toUtm(zoneOverride);
return new Utm_Mgrs(utm.zone, utm.hemisphere, utm.easting, utm.northing, utm.datum, utm.convergence, utm.scale);
}
}
/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
export { Mgrs as default, Utm_Mgrs as Utm, Latlon_Utm_Mgrs as LatLon, Dms };