//JS 实现的WGS84 坐标系转火星坐标系 GCJ-02 转百度坐标系 BD-09

function _transformLat(x, y) {
    var ret = -100.0 + 2.0 * x + 3.0 * y + 0.2 * y * y + 0.1 * x * y + 0.2 * Math.sqrt(Math.abs(x));
    ret += (20.0 * Math.sin(6.0 * x * Math.PI) + 20.0 * Math.sin(2.0 * x * Math.PI)) * 2.0 / 3.0;
    ret += (20.0 * Math.sin(y * Math.PI) + 40.0 * Math.sin(y / 3.0 * Math.PI)) * 2.0 / 3.0;
    ret += (160.0 * Math.sin(y / 12.0 * Math.PI) + 320 * Math.sin(y * Math.PI / 30.0)) * 2.0 / 3.0;
    return ret;
}

function _transformLon(x, y) {
    var ret = 300.0 + x + 2.0 * y + 0.1 * x * x + 0.1 * x * y + 0.1 * Math.sqrt(Math.abs(x));
    ret += (20.0 * Math.sin(6.0 * x * Math.PI) + 20.0 * Math.sin(2.0 * x * Math.PI)) * 2.0 / 3.0;
    ret += (20.0 * Math.sin(x * Math.PI) + 40.0 * Math.sin(x / 3.0 * Math.PI)) * 2.0 / 3.0;
    ret += (150.0 * Math.sin(x / 12.0 * Math.PI) + 300.0 * Math.sin(x / 30.0 * Math.PI)) * 2.0 / 3.0;
    return ret;
}

function gps84ToGcj02(lon, lat) {
    var a = 6378245.0;
    var ee = 0.00669342162296594323;
    var dLat = _transformLat(lon - 105.0, lat - 35.0);
    var dLon = _transformLon(lon - 105.0, lat - 35.0);
    var radLat = lat / 180.0 * Math.PI;
    var magic = Math.sin(radLat);
    magic = 1 - ee * magic * magic;
    var sqrtMagic = Math.sqrt(magic);
    dLat = (dLat * 180.0) / ((a * (1 - ee)) / (magic * sqrtMagic) * Math.PI);
    dLon = (dLon * 180.0) / (a / sqrtMagic * Math.cos(radLat) * Math.PI);
    var mgLat = lat + dLat;
    var mgLon = lon + dLon;
    return [mgLon, mgLat];
}

function gcj02ToBd09(gg_lon, gg_lat) {
    var x = gg_lon, y = gg_lat;
    var z = Math.sqrt(x * x + y * y) + 0.00002 * Math.sin(y * Math.PI);
    var theta = Math.atan2(y, x) + 0.000003 * Math.cos(x * Math.PI);
    var bd_lon = z * Math.cos(theta) + 0.0065;
    var bd_lat = z * Math.sin(theta) + 0.006;
    return [bd_lon, bd_lat];
}

function gps84ToBd09(lon, lat) {
    var p1 = gps84ToGcj02(lon, lat);
    return gcj02ToBd09(p1[0], p1[1]);
}