How to convert Lat & Long from Onemap.sg to Google Maps

Question

I have a set of address for Singapore, I would like to take the Lat & Long from onemap.sg (SYV21: X, Y / Easting, Northing) and then store it in my databse , convert into (WGS84: Longitude, Latitude) used by google maps and then display on Google Maps.

I have looked at this -- http://sgonemap.codeplex.com/ but could not get much out of it.

It will be really nice if someone can help me on this.

Answer 1

try https://github.com/singachea/Onemap-SVY21-API

Answer 2

This information maybe outdated. If you guys want to use SVY21 to WGS84 Conversion, try: https://docs.onemap.sg/#3414-svy21-to-4326-wgs84

Answer 3

JavaScript example:

import proj4 from 'proj4'
proj4.defs("EPSG:3414","+proj=tmerc +lat_0=1.366666666666667 +lon_0=103.8333333333333 +k=1 +x_0=28001.642 +y_0=38744.572 +ellps=WGS84 +units=m +no_defs");
var coords = proj4("EPSG:3414").inverse([43387.0213,40582.6686]);
console.log(coords)

Projection details were retrieved from https://epsg.io/3414

Answer 4

Try this one, https://github.com/cgcai/SVY21

Source is there,

A sample in JavaScript code is shown below (Author/s has not put any licence info on the script but has stated as free and open source in readme):

var SVY21 = (function(){
    // Ref: http://www.linz.govt.nz/geodetic/conversion-coordinates/projection-conversions/transverse-mercator-preliminary-computations/index.aspx
    
    // WGS84 Datum
    this.a = 6378137;
    this.f = 1 / 298.257223563;

    // SVY21 Projection
    // Fundamental point: Base 7 at Pierce Resevoir.
    // Latitude: 1 22 02.9154 N, longitude: 103 49 31.9752 E (of Greenwich).

    // Known Issue: Setting (oLat, oLon) to the exact coordinates specified above
// results in computation being slightly off. The values below give the most
    // accurate represenation of test data.
    this.oLat = 1.366666; // origin's lat in degrees
    this.oLon = 103.833333; // origin's lon in degrees
    this.oN = 38744.572; // false Northing
this.oE = 28001.642; // false Easting
    this.k = 1; // scale factor

    this.init = function(){
  
        this.b = this.a * (1 - this.f);
        this.e2 = (2 * this.f) - (this.f * this.f);
        this.e4 = this.e2 * this.e2;
        this.e6 = this.e4 * this.e2;
        this.A0 = 1 - (this.e2 / 4) - (3 * this.e4 / 64) - (5 * this.e6 / 256);
        this.A2 = (3. / 8.) * (this.e2 + (this.e4 / 4) + (15 * this.e6 / 128));
        this.A4 = (15. / 256.) * (this.e4 + (3 * this.e6 / 4));
        this.A6 = 35 * this.e6 / 3072;
};
this.init();

    this.computeSVY21 = function(lat, lon){
        //Returns a pair (N, E) representing Northings and Eastings in SVY21.

        var latR = lat * Math.PI / 180;
        var sinLat = Math.sin(latR);
        var sin2Lat = sinLat * sinLat;
        var cosLat = Math.cos(latR);
        var cos2Lat = cosLat * cosLat;
        var cos3Lat = cos2Lat * cosLat;
        var cos4Lat = cos3Lat * cosLat;
        var cos5Lat = cos4Lat * cosLat;
        var cos6Lat = cos5Lat * cosLat;
        var cos7Lat = cos6Lat * cosLat;

        var rho = this.calcRho(sin2Lat);
        var v = this.calcV(sin2Lat);
        var psi = v / rho;
        var t = Math.tan(latR);
        var w = (lon - this.oLon) * Math.PI / 180;

        var M = this.calcM(lat);
        var Mo = this.calcM(this.oLat);

        var w2 = w * w;
        var w4 = w2 * w2;
        var w6 = w4 * w2;
        var w8 = w6 * w2;

        var psi2 = psi * psi;
        var psi3 = psi2 * psi;
        var psi4 = psi3 * psi;

        var t2 = t * t;
        var t4 = t2 * t2;
        var t6 = t4 * t2;

        // Compute Northing
        var nTerm1 = w2 / 2 * v * sinLat * cosLat;
        var nTerm2 = w4 / 24 * v * sinLat * cos3Lat * (4 * psi2 + psi - t2);
        var nTerm3 = w6 / 720 * v * sinLat * cos5Lat * ((8 * psi4) * (11 - 24 * t2) - (28 * psi3) * (1 - 6 * t2) + psi2 * (1 - 32 * t2) - psi * 2 * t2 + t4);
        var nTerm4 = w8 / 40320 * v * sinLat * cos7Lat * (1385 - 3111 * t2 + 543 * t4 - t6);
        var N = this.oN + this.k * (M - Mo + nTerm1 + nTerm2 + nTerm3 + nTerm4);

        // Compute Easting
        var eTerm1 = w2 / 6 * cos2Lat * (psi - t2);
        var eTerm2 = w4 / 120 * cos4Lat * ((4 * psi3) * (1 - 6 * t2) + psi2 * (1 + 8 * t2) - psi * 2 * t2 + t4);
        var eTerm3 = w6 / 5040 * cos6Lat * (61 - 479 * t2 + 179 * t4 - t6);
        var E = this.oE + this.k * v * w * cosLat * (1 + eTerm1 + eTerm2 + eTerm3);

        return {N:N, E:E};
};



this.calcM = function(lat, lon){
        var latR = lat * Math.PI / 180;
        return this.a * ((this.A0 * latR) - (this.A2 * Math.sin(2 * latR)) + (this.A4 * Math.sin(4 * latR)) - (this.A6 * Math.sin(6 * latR)));
};

    this.calcRho = function(sin2Lat){
        var num = this.a * (1 - this.e2);
        var denom = Math.pow(1 - this.e2 * sin2Lat, 3. / 2.);
        return num / denom;
};

    this.calcV = function(sin2Lat){
        var poly = 1 - this.e2 * sin2Lat;
        return this.a / Math.sqrt(poly);
};



    this.computeLatLon = function(N, E){
        // Returns a pair (lat, lon) representing Latitude and Longitude.
        

        var Nprime = N - this.oN;
        var Mo = this.calcM(this.oLat);
        var Mprime = Mo + (Nprime / this.k);
        var n = (this.a - this.b) / (this.a + this.b);
        var n2 = n * n;
        var n3 = n2 * n;
        var n4 = n2 * n2;
        var G = this.a * (1 - n) * (1 - n2) * (1 + (9 * n2 / 4) + (225 * n4 / 64)) * (Math.PI / 180);
        var sigma = (Mprime * Math.PI) / (180. * G);
        
        var latPrimeT1 = ((3 * n / 2) - (27 * n3 / 32)) * Math.sin(2 * sigma);
        var latPrimeT2 = ((21 * n2 / 16) - (55 * n4 / 32)) * Math.sin(4 * sigma);
        var latPrimeT3 = (151 * n3 / 96) * Math.sin(6 * sigma);
        var latPrimeT4 = (1097 * n4 / 512) * Math.sin(8 * sigma);
        var latPrime = sigma + latPrimeT1 + latPrimeT2 + latPrimeT3 + latPrimeT4;

        var sinLatPrime = Math.sin(latPrime);
        var sin2LatPrime = sinLatPrime * sinLatPrime;

        var rhoPrime = this.calcRho(sin2LatPrime);
        var vPrime = this.calcV(sin2LatPrime);
        var psiPrime = vPrime / rhoPrime;
        var psiPrime2 = psiPrime * psiPrime;
        var psiPrime3 = psiPrime2 * psiPrime;
        var psiPrime4 = psiPrime3 * psiPrime;
        var tPrime = Math.tan(latPrime);
        var tPrime2 = tPrime * tPrime;
        var tPrime4 = tPrime2 * tPrime2;
        var tPrime6 = tPrime4 * tPrime2;
        var Eprime = E - this.oE;
        var x = Eprime / (this.k * vPrime);
        var x2 = x * x;
        var x3 = x2 * x;
        var x5 = x3 * x2;
        var x7 = x5 * x2;

        // Compute Latitude
        var latFactor = tPrime / (this.k * rhoPrime);
        var latTerm1 = latFactor * ((Eprime * x) / 2);
        var latTerm2 = latFactor * ((Eprime * x3) / 24) * ((-4 * psiPrime2) + (9 * psiPrime) * (1 - tPrime2) + (12 * tPrime2));
        var latTerm3 = latFactor * ((Eprime * x5) / 720) * ((8 * psiPrime4) * (11 - 24 * tPrime2) - (12 * psiPrime3) * (21 - 71 * tPrime2) + (15 * psiPrime2) * (15 - 98 * tPrime2 + 15 * tPrime4) + (180 * psiPrime) * (5 * tPrime2 - 3 * tPrime4) + 360 * tPrime4);
        var latTerm4 = latFactor * ((Eprime * x7) / 40320) * (1385 - 3633 * tPrime2 + 4095 * tPrime4 + 1575 * tPrime6);
        var lat = latPrime - latTerm1 + latTerm2 - latTerm3 + latTerm4;

        // Compute Longitude
        var secLatPrime = 1. / Math.cos(lat);
        var lonTerm1 = x * secLatPrime;
        var lonTerm2 = ((x3 * secLatPrime) / 6) * (psiPrime + 2 * tPrime2);
        var lonTerm3 = ((x5 * secLatPrime) / 120) * ((-4 * psiPrime3) * (1 - 6 * tPrime2) + psiPrime2 * (9 - 68 * tPrime2) + 72 * psiPrime * tPrime2 + 24 * tPrime4);
        var lonTerm4 = ((x7 * secLatPrime) / 5040) * (61 + 662 * tPrime2 + 1320 * tPrime4 + 720 * tPrime6);
        var lon = (this.oLon * Math.PI / 180) + lonTerm1 - lonTerm2 + lonTerm3 - lonTerm4;

        return {lat: lat / (Math.PI / 180), lon: lon / (Math.PI / 180)};
};

});

Answer 5

Please refer to this example in PHP.