Loiste

WGS84 to KKJ in JavaScript

In order to use the YTV route planning API, one has to convert coordinates from the system the device uses (WGS84) to the legacy Finnish one, KKJ. We implemented our own library in JavaScript since there was none available. It is more or less loosely based on a number of other implementations which seem to have a common origin.

Our implementation is licensed under the same permissive license as the rest of our project. The license is MIT. Thanks go to Matti Aarnio for this. And here is the source: wgs84tokkj.js.

/**
 * Based on Matti Aarnio´s convertion algorithms
 *  <http://www.viestikallio.fi/tools/kkj-wgs84.php>
 * 
 * Licensed under MIT with Matti Aarnio's permission.
 * 
 * @license MIT (see ../license.txt)
 */

var wgsCon = {
	rad2deg: function(rad){
		return (rad / (Math.PI)) * 180;
	},
	
	deg2rad: function(deg){
		return (deg * Math.PI) / 180;
	},
	
	KKJzone: function(KKJlo){
		var KKJ_ZONE = [18.0, 21.0, 24.0, 27.0, 30.0, 33.0];
		var ZoneNumber = 0;
		while (ZoneNumber <= 5) {
			if (Math.abs(KKJlo - KKJ_ZONE[ZoneNumber]) <= 1.5) {
				break;
			}
			ZoneNumber = ZoneNumber + 1;
		}
		return ZoneNumber;
	},
	
	WGSlalo_to_KKJlalo: function(WGS){
		var La = WGS[0];
		var Lo = WGS[1];
		var dLa = wgsCon.deg2rad(-0.124766E+01 + 0.269941E+00 * La - 0.191342E+00 * Lo - 0.356086E-02 * La * La + 0.122353E-02 * La * Lo + 0.335456E-03 * Lo * Lo) / 3600.0;
		var dLo = wgsCon.deg2rad(0.286008E+02 - 0.114139E+01 * La + 0.581329E+00 * Lo + 0.152376E-01 * La * La - 0.118166E-01 * La * Lo - 0.826201E-03 * Lo * Lo) / 3600.0;
		var KKJla = wgsCon.rad2deg(wgsCon.deg2rad(La) + dLa);
		var KKJlo = wgsCon.rad2deg(wgsCon.deg2rad(Lo) + dLo);
		var KKJ = [KKJla, KKJlo];
		return KKJ;
	},
	
	KKJlalo_to_KKJxy: function(INP, ZoneNumber){
		var KKJ_ZONE = [18.0, 21.0, 24.0, 27.0, 30.0, 33.0];
		var Lo = (wgsCon.deg2rad(INP[1]) - wgsCon.deg2rad(KKJ_ZONE[ZoneNumber]));
		var a = 6378388.0; // Hayford ellipsoid
		var f = 1 / 297.0;
		var b = (1.0 - f) * a;
		var bb = b * b;
		var c = (a / b) * a;
		var ee = (a * a - bb) / bb;
		var n = (a - b) / (a + b);
		var nn = n * n;
		var cosLa = Math.cos(wgsCon.deg2rad(INP[0]));
		var NN = ee * cosLa * cosLa;
		var LaF = Math.atan(Math.tan(wgsCon.deg2rad(INP[0])) / Math.cos(Lo * Math.sqrt(1 + NN)));
		var cosLaF = Math.cos(LaF);
		var t = (Math.tan(Lo) * cosLaF) / Math.sqrt(1 + ee * cosLaF * cosLaF);
		var A = a / (1 + n);
		var A1 = A * (1 + nn / 4 + nn * nn / 64);
		var A2 = A * 1.5 * n * (1 - nn / 8);
		var A3 = A * 0.9375 * nn * (1 - nn / 4);
		var A4 = A * 35 / 48.0 * nn * n;
		var OUT = [0, 0];
		OUT[0] = A1 * LaF - A2 * Math.sin(2 * LaF) + A3 * Math.sin(4 * LaF) - A4 * Math.sin(6 * LaF);
		OUT[1] = c * Math.log(t + Math.sqrt(1 + t * t)) + 500000.0 + ZoneNumber * 1000000.0;
		return OUT;
	},
	
	WGS84lalo_to_KKJxy: function(lat, lon){
		var wgs84 = [lat, lon];
		
		var KKJlalo = wgsCon.WGSlalo_to_KKJlalo(wgs84);
		var ZoneNumber = wgsCon.KKJzone(KKJlalo[1]);
		var KKJxy = wgsCon.KKJlalo_to_KKJxy(KKJlalo, ZoneNumber)
		return KKJxy;
	}
}