在我國，為了國家安全，電子地圖不可以使用地球座標系WGS84，必須經過偏轉。面前主流的幾款地圖都有其對應的座標系。

例如

高德、騰訊、圖靈、阿里地圖等都是 GCJ-02座標系（也稱火星座標系）

而百度則使用BD-09座標系。

那麼這3個常用座標系直接如何轉換呢。

參照這個連線我總結了一下。http://blog.csdn.net/meegomeego/article/details/39927017

1，GCJ-02(火星)轉BD-09（百度地圖）

邏輯：

void bd_encrypt(double gg_lat, double gg_lon, double &bd_lat, double &bd_lon)
{
    double x = gg_lon, y = gg_lat;
    double z = sqrt(x * x + y * y) + 0.00002 * sin(y * x_pi);
    double theta = atan2(y, x) + 0.000003 * cos(x * x_pi);
    bd_lon = z * cos(theta) + 0.0065;
    bd_lat = z * sin(theta) + 0.006;
}
 

function MapabcEncryptToBdmap(gg_lat, gg_lon)  
 {  
	  
	 var point=new Object();
	 var x_pi = 3.14159265358979324 * 3000.0 / 180.0;
     var x = new Number(gg_lon);
     var y = new Number(gg_lat);  
     var z =  Math.sqrt(x * x + y * y) + 0.00002 * Math.sin(y * x_pi);  
     var theta = Math.atan2(y, x) + 0.000003 * Math.cos(x * x_pi);  
     var bd_lon = z * Math.cos(theta) + 0.0065;  
     var bd_lat = z * Math.sin(theta) + 0.006; 
     point.lng=bd_lon;
     point.lat=bd_lat;
     //alert("-1:"+point.lng+","+point.lat);
     return point;
 }  
 

邏輯：

void bd_decrypt(double bd_lat, double bd_lon, double &gg_lat, double &gg_lon)
{
    double x = bd_lon - 0.0065, y = bd_lat - 0.006;
    double z = sqrt(x * x + y * y) - 0.00002 * sin(y * x_pi);
    double theta = atan2(y, x) - 0.000003 * cos(x * x_pi);
    gg_lon = z * cos(theta);
    gg_lat = z * sin(theta);
}
 

 function BdmapEncryptToMapabc(bd_lat,bd_lon)
 {
	 var point=new Object();
	 var x_pi = 3.14159265358979324 * 3000.0 / 180.0;
     var x = new Number(bd_lon - 0.0065);
     var y = new Number(bd_lat - 0.006);
     var z = Math.sqrt(x * x + y * y) - 0.00002 * Math.sin(y * x_pi);
     var theta = Math.atan2(y, x) - 0.000003 * Math.cos(x * x_pi);
     var Mars_lon = z * Math.cos(theta);
     var Mars_lat = z * Math.sin(theta);
     point.lng=Mars_lon;
     point.lat=Mars_lat;
     return point;
 }

3，WGS84(地球座標系)轉BD-09(百度座標系)

	function GPSToBaidu(lngX,latY){
		var gps_point=new BMap.Point(lngX,latY);
		BMap.Convertor.translate(gps_point,0,function(bd_point){  		
			 alert("lng:"+bd_point.lng+" lat:"+bd_point.lat);
		});
	}

邏輯C#版（幹活了，沒時間了）：

using System;

namespace Navi
{
    class EvilTransform
    {
        const double pi = 3.14159265358979324;

        //
        // Krasovsky 1940
        //
        // a = 6378245.0, 1/f = 298.3
        // b = a * (1 - f)
        // ee = (a^2 - b^2) / a^2;
        const double a = 6378245.0;
        const double ee = 0.00669342162296594323;

        //
        // World Geodetic System ==> Mars Geodetic System
        public static void transform(double wgLat, double wgLon, out double mgLat, out double mgLon)
        {
            if (outOfChina(wgLat, wgLon))
            {
                mgLat = wgLat;
                mgLon = wgLon;
                return;
            }
            double dLat = transformLat(wgLon - 105.0, wgLat - 35.0);
            double dLon = transformLon(wgLon - 105.0, wgLat - 35.0);
            double radLat = wgLat / 180.0 * pi;
            double magic = Math.Sin(radLat);
            magic = 1 - ee * magic * magic;
            double sqrtMagic = Math.Sqrt(magic);
            dLat = (dLat * 180.0) / ((a * (1 - ee)) / (magic * sqrtMagic) * pi);
            dLon = (dLon * 180.0) / (a / sqrtMagic * Math.Cos(radLat) * pi);
            mgLat = wgLat + dLat;
            mgLon = wgLon + dLon;
        }

        static bool outOfChina(double lat, double lon)
        {
            if (lon < 72.004 || lon > 137.8347)
                return true;
            if (lat < 0.8293 || lat > 55.8271)
                return true;
            return false;
        }

        static double transformLat(double x, double y)
        {
            double 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 * pi) + 20.0 * Math.Sin(2.0 * x * pi)) * 2.0 / 3.0;
            ret += (20.0 * Math.Sin(y * pi) + 40.0 * Math.Sin(y / 3.0 * pi)) * 2.0 / 3.0;
            ret += (160.0 * Math.Sin(y / 12.0 * pi) + 320 * Math.Sin(y * pi / 30.0)) * 2.0 / 3.0;
            return ret;
        }

        static double transformLon(double x, double y)
        {
            double 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 * pi) + 20.0 * Math.Sin(2.0 * x * pi)) * 2.0 / 3.0;
            ret += (20.0 * Math.Sin(x * pi) + 40.0 * Math.Sin(x / 3.0 * pi)) * 2.0 / 3.0;
            ret += (150.0 * Math.Sin(x / 12.0 * pi) + 300.0 * Math.Sin(x / 30.0 * pi)) * 2.0 / 3.0;
            return ret;
        }
    }
}

關於準確性，BD-09和GCJ-02我驗證過了，誤差在10米左右，可以接收。WGS-84和其他座標系直接的轉換待完善和驗證。