utmconv.js

/* 
 * JS functions for converting between UTM and geographic coordinates and
 * vice versa.
 * 
 * @author Po Shan Cheah http://mortonfox.com
 *
 * Based on http://www.uwgb.edu/dutchs/UsefulData/UTMFormulas.htm
 * by Dr. Steve Dutch.
 *
 * This program is free software: you can redistribute it and/or modify it
 * under the terms of the GNU Lesser General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or (at your
 * option) any later version.
 *
 * This program is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public
 * License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */
/*jslint vars: true, white: true */

var UTMConv = (function () {
	"use strict";

	var DatumInfo = {
	    wgs84         : { eqrad : 6378137.0, flat : 298.2572236 },
	    nad83         : { eqrad : 6378137.0, flat : 298.2572236 },
	    grs80         : { eqrad : 6378137.0, flat : 298.2572215 },
	    wgs72         : { eqrad : 6378135.0, flat : 298.2597208 },
	    aust1965      : { eqrad : 6378160.0, flat : 298.2497323 },
	    krasovsky1940 : { eqrad : 6378245.0, flat : 298.2997381 },
	    na1927        : { eqrad : 6378206.4, flat : 294.9786982 },
	    intl1924      : { eqrad : 6378388.0, flat : 296.9993621 },
	    hayford1909   : { eqrad : 6378388.0, flat : 296.9993621 },
	    clarke1880    : { eqrad : 6378249.1, flat : 293.4660167 },
	    clarke1866    : { eqrad : 6378206.4, flat : 294.9786982 },
	    airy1830      : { eqrad : 6377563.4, flat : 299.3247788 },
	    bessel1841    : { eqrad : 6377397.2, flat : 299.1527052 },
	    everest1830   : { eqrad : 6377276.3, flat : 300.8021499 }
	};

	function UTMCoords(utmz, easting, northing) {
	    this.utmz = utmz;
	    this.easting = easting;
	    this.northing = northing;
	}

	UTMCoords.prototype.toString = function () {
	    return "Zone " + this.utmz + " Easting " + this.easting + " Northing " + this.northing;
	};

	function DegCoords(latd, lngd, datum) {
	    this.latd = latd;
	    this.lngd = lngd;
	    this.datum = datum || "wgs84";
	}

	DegCoords.prototype.calc_utmz = function () {
	    // Calculate utm zone.
	    return 1 + Math.floor((this.lngd + 180) / 6);
	};

	DegCoords.prototype.toString = function () {
	    return this.latd + ", " + this.lngd;
	};

	DegCoords.prototype.to_utm = function (utmz) {
	    // Convert to UTM. If utmz is not supplied, calculate it during the
	    // conversion.
	    var a = DatumInfo[this.datum].eqrad;//equatorial radius, meters. 
	    var f = 1 / DatumInfo[this.datum].flat;//polar flattening.

	    var drad = Math.PI/180;//Convert degrees to radians)
	    var k0 = 0.9996;//scale on central meridian
	    var b = a*(1-f);//polar axis.
	    var e = Math.sqrt(1 - (b/a)*(b/a));//eccentricity

	    var phi = this.latd*drad;//Convert latitude to radians
	    // var lng = lngd*drad;//Convert longitude to radians

	    utmz = utmz || this.calc_utmz();

	    // var latz = 0;//Latitude zone: A-B S of -80, C-W -80 to +72, X 72-84, Y,Z N of 84
	    // if (latd > -80 && latd < 72){latz = Math.floor((latd + 80)/8)+2;}
	    // if (latd > 72 && latd < 84){latz = 21;}
	    // if (latd > 84){latz = 23;}

	    var zcm = 3 + 6*(utmz-1) - 180;//Central meridian of zone
	    // var e0 = e/Math.sqrt(1 - e*e);//Called e prime in reference
	    var esq = (1 - (b/a)*(b/a));//e squared for use in expansions
	    var e0sq = e*e/(1-e*e);// e0 squared - always even powers

	    var N = a/Math.sqrt(1-Math.pow(e*Math.sin(phi),2));
	    var T = Math.pow(Math.tan(phi),2);
	    var C = e0sq*Math.pow(Math.cos(phi),2);
	    var A = (this.lngd-zcm)*drad*Math.cos(phi);

	    var M = phi*(1 - esq*(1/4 + esq*(3/64 + 5*esq/256)));
	    M = M - Math.sin(2*phi)*(esq*(3/8 + esq*(3/32 + 45*esq/1024)));
	    M = M + Math.sin(4*phi)*(esq*esq*(15/256 + esq*45/1024));
	    M = M - Math.sin(6*phi)*(esq*esq*esq*(35/3072));
	    M = M*a;//Arc length along standard meridian

	    var M0 = 0;//M0 is M for some origin latitude other than zero. Not needed for standard UTM

	    var x = k0*N*A*(1 + A*A*((1-T+C)/6 + A*A*(5 - 18*T + T*T + 72*C -58*e0sq)/120));//Easting relative to CM
	    x = x + 500000; //Easting standard 
	    var y = k0*(M - M0 + N*Math.tan(phi)*(A*A*(1/2 + A*A*((5 - T + 9*C + 4*C*C)/24 + A*A*(61 - 58*T + T*T + 600*C - 330*e0sq)/720))));//Northing from equator
	    // var yg = y + 10000000;//yg = y global, from S. Pole

	    // Let negative values stand for southern hemisphere.
	    //if (y < 0){y = 10000000+y;}

	    return new UTMCoords(utmz, x, y);
	};

	UTMCoords.prototype.to_degmin = function (datum) {
	    return this.to_deg(datum).to_degmin();
	};

	UTMCoords.prototype.to_deg = function (datum) {
	    // Convert UTM coords to Deg coords. If datum is unspecified,
	    // default to wgs84.

	    datum = datum || "wgs84";

	    var a = DatumInfo[datum].eqrad;//equatorial radius, meters. 
	    var f = 1 / DatumInfo[datum].flat;//polar flattening.

	    var drad = Math.PI/180;//Convert degrees to radians)
	    var k0 = 0.9996;//scale on central meridian
	    var b = a*(1-f);//polar axis.
	    var e = Math.sqrt(1 - (b/a)*(b/a));//eccentricity
	    // var e0 = e/Math.sqrt(1 - e*e);//Called e prime in reference
	    var esq = (1 - (b/a)*(b/a));//e squared for use in expansions
	    var e0sq = e*e/(1-e*e);// e0 squared - always even powers

	    var x = this.easting;
	    var y = this.northing;

	    var zcm = 3 + 6*(this.utmz-1) - 180;//Central meridian of zone
	    var e1 = (1 - Math.sqrt(1 - e*e))/(1 + Math.sqrt(1 - e*e));//Called e1 in USGS PP 1395 also
	    var M0 = 0;//In case origin other than zero lat - not needed for standard UTM
	    var M = M0 + y/k0;//Arc length along standard meridian. 

	    var mu = M/(a*(1 - esq*(1/4 + esq*(3/64 + 5*esq/256))));
	    var phi1 = mu + e1*(3/2 - 27*e1*e1/32)*Math.sin(2*mu) + e1*e1*(21/16 -55*e1*e1/32)*Math.sin(4*mu);//Footprint Latitude
	    phi1 = phi1 + e1*e1*e1*(Math.sin(6*mu)*151/96 + e1*Math.sin(8*mu)*1097/512);
	    var C1 = e0sq*Math.pow(Math.cos(phi1),2);
	    var T1 = Math.pow(Math.tan(phi1),2);
	    var N1 = a/Math.sqrt(1-Math.pow(e*Math.sin(phi1),2));
	    var R1 = N1*(1-e*e)/(1-Math.pow(e*Math.sin(phi1),2));

	    var D = (x-500000)/(N1*k0);
	    var phi = (D*D)*(1/2 - D*D*(5 + 3*T1 + 10*C1 - 4*C1*C1 - 9*e0sq)/24);
	    phi = phi + Math.pow(D,6)*(61 + 90*T1 + 298*C1 + 45*T1*T1 -252*e0sq - 3*C1*C1)/720;
	    phi = phi1 - (N1*Math.tan(phi1)/R1)*phi;

	    var lng = D*(1 + D*D*((-1 -2*T1 -C1)/6 + D*D*(5 - 2*C1 + 28*T1 - 3*C1*C1 +8*e0sq + 24*T1*T1)/120))/Math.cos(phi1);
	    var lngd = zcm+lng/drad;

	    return new DegCoords(phi/drad, lngd, datum);
	};

	function DegMinCoords(latdir, latdeg, latmin, lngdir, lngdeg, lngmin, datum) {
	    this.datum = datum || "wgs84";
	    this.latdir = latdir;
	    this.latdeg = latdeg;
	    this.latmin = latmin;
	    this.lngdir = lngdir;
	    this.lngdeg = lngdeg;
	    this.lngmin = lngmin;
	}

	DegCoords.prototype.to_degmin = function () {
	    // Convert degree format to degree and minutes format.

	    var latd = this.latd;
	    var lngd = this.lngd;

	    var latdir = "N";
	    if (latd < 0) {
		latdir = "S";
		latd = -latd;
	    }
	    var latdeg = Math.floor(latd);
	    var latmin = 60.0 * (latd - latdeg);

	    var lngdir = "E";
	    if (lngd < 0) {
		lngdir = "W";
		lngd = -lngd;
	    }
	    var lngdeg = Math.floor(lngd);
	    var lngmin = 60.0 * (lngd - lngdeg);

	    return new DegMinCoords(latdir, latdeg, latmin, lngdir, lngdeg, lngmin, this.datum);
	};

	DegMinCoords.prototype.to_utm = function (utmz) {
	    return this.to_deg().to_utm(utmz);
	};

	DegMinCoords.prototype.to_deg = function () {
	    // Convert degree and minutes format to degree format.
	    
	    var latd = this.latdeg + this.latmin / 60.0;
	    if ("S" === this.latdir || "s" === this.latdir) {
		latd = -latd;
	    }
	    var lngd = this.lngdeg + this.lngmin / 60.0;
	    if ("W" === this.lngdir || "w" === this.lngdir) {
		lngd = -lngd;
	    }
	    return new DegCoords(latd, lngd, this.datum);
	};

	DegMinCoords.prototype.toString = function () {
	    return this.latdir + " " + this.latdeg + " " + this.latmin + " " + this.lngdir + " " + this.lngdeg + " " + this.lngmin;
	};

	return { UTMCoords : UTMCoords, DegCoords : DegCoords, DegMinCoords : DegMinCoords };
    }());