GPS坐标互转：WGS-84(GPS)、GCJ-02(Google地图)、BD-09(百度地图)

WGS-84：是国际标准，GPS坐标（Google Earth使用、或者GPS模块）
GCJ-02：中国坐标偏移标准，Google Map、高德、腾讯使用
BD-09：百度坐标偏移标准，Baidu Map使用

//WGS-84 to GCJ-02
GPS.gcj_encrypt();

//GCJ-02 to WGS-84 粗略
GPS.gcj_decrypt();

//GCJ-02 to WGS-84 精确(二分极限法)
// var threshold = 0.000000001; 目前设置的是精确到小数点后9位，这个值越小，越精确，但是javascript中，浮点运算本身就不太精确，九位在GPS里也偏差不大了
GSP.gcj_decrypt_exact();

//GCJ-02 to BD-09
GPS.bd_encrypt();

//BD-09 to GCJ-02
GPS.bd_decrypt();

//求距离
GPS.distance();

示例：
document.write("GPS: 39.933676862706776,116.35608315379092<br />");
var arr2 = GPS.gcj_encrypt(39.933676862706776, 116.35608315379092);
document.write("中国:" + arr2['lat']+","+arr2['lon']+'<br />');
var arr3 = GPS.gcj_decrypt_exact(arr2['lat'], arr2['lon']);
document.write('逆算:' + arr3['lat']+","+arr3['lon']+' 需要和第一行相似（目前是小数点后9位相等）');

var GPS = {
PI : 3.14159265358979324,
x_pi : 3.14159265358979324 * 3000.0 / 180.0,
delta : function (lat, lon)
{
// Krasovsky 1940
//
// a = 6378245.0, 1/f = 298.3
// b = a * (1 - f)
// ee = (a^2 - b^2) / a^2;
var a = 6378245.0;
var ee = 0.00669342162296594323;
var dLat = this.transformLat(lon - 105.0, lat - 35.0);
var dLon = this.transformLon(lon - 105.0, lat - 35.0);
var radLat = lat / 180.0 * this.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) * this.PI);
dLon = (dLon * 180.0) / (a / sqrtMagic * Math.cos(radLat) * this.PI);
return {'lat': dLat, 'lon': dLon};
},
//WGS-84 to GCJ-02
gcj_encrypt : function (wgsLat, wgsLon)
{
if (this.outOfChina(wgsLat, wgsLon))
return {'lat': wgsLat, 'lon': wgsLon};

var d = this.delta(wgsLat, wgsLon);
return {'lat' : wgsLat + d.lat,'lon' : wgsLon + d.lon};
},
//GCJ-02 to WGS-84
gcj_decrypt : function (gcjLat, gcjLon)
{
if (this.outOfChina(gcjLat, gcjLon))
return {'lat': gcjLat, 'lon': gcjLon};

var d = this.delta(gcjLat, gcjLon);
return {'lat': gcjLat - d.lat, 'lon': gcjLon - d.lon};
},
//GCJ-02 to WGS-84 exactly
gcj_decrypt_exact : function (gcjLat, gcjLon) {
var initDelta = 0.01;
var threshold = 0.000000001;
var dLat = initDelta, dLon = initDelta;
var mLat = gcjLat - dLat, mLon = gcjLon - dLon;
var pLat = gcjLat + dLat, pLon = gcjLon + dLon;
var wgsLat, wgsLon, i = 0;
while (1) {
wgsLat = (mLat + pLat) / 2;
wgsLon = (mLon + pLon) / 2;
var tmp = this.gcj_encrypt(wgsLat, wgsLon)
dLat = tmp.lat - gcjLat;
dLon = tmp.lon - gcjLon;
if ((Math.abs(dLat) < threshold) && (Math.abs(dLon) < threshold))
break;

if (dLat > 0) pLat = wgsLat; else mLat = wgsLat;
if (dLon > 0) pLon = wgsLon; else mLon = wgsLon;

if (++i > 10000) break;
}
//console.log(i);
return {'lat': wgsLat, 'lon': wgsLon};
},
//GCJ-02 to BD-09
bd_encrypt : function (gcjLat, gcjLon)
{
var x = gcjLon, y = gcjLat; 
var z = Math.sqrt(x * x + y * y) + 0.00002 * Math.sin(y * this.x_pi); 
var theta = Math.atan2(y, x) + 0.000003 * Math.cos(x * this.x_pi); 
bdLon = z * Math.cos(theta) + 0.0065; 
bdLat = z * Math.sin(theta) + 0.006; 
return {'lat' : bdLat,'lon' : bdLon};
},
//BD-09 to GCJ-02
bd_decrypt : function (bdLat, bdLon)
{
var x = bdLon - 0.0065, y = bdLat - 0.006; 
var z = Math.sqrt(x * x + y * y) - 0.00002 * Math.sin(y * this.x_pi); 
var theta = Math.atan2(y, x) - 0.000003 * Math.cos(x * this.x_pi); 
var gcjLon = z * Math.cos(theta); 
var gcjLat = z * Math.sin(theta);
return {'lat' : gcjLat, 'lon' : gcjLon};
},
distance : function (latA, logA, latB, logB) {
var earthR = 6371000;
var x = Math.cos(latA*Math.PI/180) * Math.cos(latB*Math.PI/180) * Math.cos((logA-logB)*Math.PI/180);
var y = Math.sin(latA*Math.PI/180) * Math.sin(latB*Math.PI/180);
var s = x + y;
if (s > 1)
s = 1;
if (s < -1)
s = -1;
var alpha = Math.acos(s);
var distance = alpha * earthR;
return distance;
},
outOfChina : function (lat, lon)
{
if (lon < 72.004 || lon > 137.8347)
return true;
if (lat < 0.8293 || lat > 55.8271)
return true;
return false;
},
transformLat : function (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 * this.PI) + 20.0 * Math.sin(2.0 * x * this.PI)) * 2.0 / 3.0;
ret += (20.0 * Math.sin(y * this.PI) + 40.0 * Math.sin(y / 3.0 * this.PI)) * 2.0 / 3.0;
ret += (160.0 * Math.sin(y / 12.0 * this.PI) + 320 * Math.sin(y * this.PI / 30.0)) * 2.0 / 3.0;
return ret;
},
transformLon : function (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 * this.PI) + 20.0 * Math.sin(2.0 * x * this.PI)) * 2.0 / 3.0;
ret += (20.0 * Math.sin(x * this.PI) + 40.0 * Math.sin(x / 3.0 * this.PI)) * 2.0 / 3.0;
ret += (150.0 * Math.sin(x / 12.0 * this.PI) + 300.0 * Math.sin(x / 30.0 * this.PI)) * 2.0 / 3.0;
return ret;
}
};