rt90 to wgs84

grid_to_geodetic.js

var axis = null;
var flattening = null;
var lat_of_origin = null;
var central_meridian = null;
var scale = null;
var false_northing = null;
var false_easting = null;

function math_cosh(value) {
    return 0.5 * (Math.exp(value) + Math.exp(-value));
}

function math_sinh(value) {
    return 0.5 * (Math.exp(value) - Math.exp(-value));
}

function sweref99_params() {
	axis = 6378137.0; // GRS 80.
	flattening = 1.0 / 298.257222101; // GRS 80.
	central_meridian = null;
	lat_of_origin = 0.0;
	scale = 1.0;
	false_northing = 0.0;
	false_easting = 150000.0;
}

function grs80_params() {
	axis = 6378137.0; // GRS 80.
	flattening = 1.0 / 298.257222101; // GRS 80.
	central_meridian = null;
	lat_of_origin = 0.0;
}

function grid_to_geodetic(projection, x, y) {
    if (projection == "rt90_2.5_gon_v") {
        grs80_params();
		central_meridian = 15.0 + 48.0/60.0 + 22.624306/3600.0;
		scale = 1.00000561024;
		false_northing = -667.711;
		false_easting = 1500064.274;
    } else if (projection == "sweref_99_tm") {
		sweref99_params();
		central_meridian = 15.00;
		lat_of_origin = 0.0;
		scale = 0.9996;
		false_northing = 0.0;
		false_easting = 500000.0;
	}

    var lat_lon = new Array(2);
    if (central_meridian == null) {
        return lat_lon;
    }
    // Prepare ellipsoid-based stuff.
    var e2 = flattening * (2.0 - flattening);
    var n = flattening / (2.0 - flattening);
    var a_roof = axis / (1.0 + n) * (1.0 + n*n/4.0 + n*n*n*n/64.0);
    var delta1 = n/2.0 - 2.0*n*n/3.0 + 37.0*n*n*n/96.0 - n*n*n*n/360.0;
    var delta2 = n*n/48.0 + n*n*n/15.0 - 437.0*n*n*n*n/1440.0;
    var delta3 = 17.0*n*n*n/480.0 - 37*n*n*n*n/840.0;
    var delta4 = 4397.0*n*n*n*n/161280.0;

    var Astar = e2 + e2*e2 + e2*e2*e2 + e2*e2*e2*e2;
    var Bstar = -(7.0*e2*e2 + 17.0*e2*e2*e2 + 30.0*e2*e2*e2*e2) / 6.0;
    var Cstar = (224.0*e2*e2*e2 + 889.0*e2*e2*e2*e2) / 120.0;
    var Dstar = -(4279.0*e2*e2*e2*e2) / 1260.0;

    // Convert.
    var deg_to_rad = Math.PI / 180;
    var lambda_zero = central_meridian * deg_to_rad;
    var xi = (x - false_northing) / (scale * a_roof);
    var eta = (y - false_easting) / (scale * a_roof);
    var xi_prim = xi -
    delta1*Math.sin(2.0*xi) * math_cosh(2.0*eta) -
    delta2*Math.sin(4.0*xi) * math_cosh(4.0*eta) -
    delta3*Math.sin(6.0*xi) * math_cosh(6.0*eta) -
    delta4*Math.sin(8.0*xi) * math_cosh(8.0*eta);
    var eta_prim = eta -
    delta1*Math.cos(2.0*xi) * math_sinh(2.0*eta) -
    delta2*Math.cos(4.0*xi) * math_sinh(4.0*eta) -
    delta3*Math.cos(6.0*xi) * math_sinh(6.0*eta) -
    delta4*Math.cos(8.0*xi) * math_sinh(8.0*eta);
    var phi_star = Math.asin(Math.sin(xi_prim) / math_cosh(eta_prim));
    var delta_lambda = Math.atan(math_sinh(eta_prim) / Math.cos(xi_prim));
    var lon_radian = lambda_zero + delta_lambda;
    var lat_radian = phi_star + Math.sin(phi_star) * Math.cos(phi_star) *
    (Astar +
        Bstar*Math.pow(Math.sin(phi_star), 2) +
        Cstar*Math.pow(Math.sin(phi_star), 4) +
        Dstar*Math.pow(Math.sin(phi_star), 6));
        lat_lon[0] = lat_radian * 180.0 / Math.PI;
        lat_lon[1] = lon_radian * 180.0 / Math.PI;

    return lat_lon;
}

console.log(grid_to_geodetic("rt90_2.5_gon_v", 6166984, 1322751));