GPS（WGS84）坐标是不能够直接放到百度地图或者google地图上的，放到百度地图或者google地图上， 会有偏移现象。所以，车载终端上传的GPS坐标需要通过纠偏来矫正这个偏移。

三种坐标

1.  GPS坐标，WGS84标准
2.  谷歌坐标=火星坐标=WGS84+GCJ02，即通过国测局发布的GCJ02标准加密后的坐标。
3.  百度坐标BD09=谷歌坐标+BD09=WGS84+GCJ02+BD09，BD09是百度自己的二次加密算法。

互转关系

百度坐标简称：BD09，谷歌坐标简称：GCJ02，GPS坐标：WGS84
1.  WGS84->GCJ02
    GPS加偏，一般的互联网地图都是GCJ02标准，如：谷歌
2.  GCJ02->BD09
    百度地图的标准
3.  WGS84->BD09
    定位到百度的GPS坐标，通过百度API会自动转换为BD09标准进行定位
4.  BD09->GCJ02
    百度坐标到火星坐标
5.  BD09->WGS84
    通过先转换到GCJ02，在通过GCJ02转换到WGS84.有精度丢失
6.  GCJ02->WGS84
    二分法逆转

部分算法

注：算法来自于网络 其中 bd_encrypt 将 GCJ-02 坐标转换成 BD-09 坐标， bd_decrypt 反之

#include <math.h>

const double x_pi = 3.14159265358979324 * 3000.0 / 180.0;

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;
}

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);
}

WGS84->GCJ02网上“公开的秘密”见https://on4wp7.codeplex.com/SourceControl/changeset/view/21483#353936

//
// Copyright (C) 1000 - 9999 Somebody Anonymous
// NO WARRANTY OR GUARANTEE
//

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;
        }
    }
}

CJ-02 到 WGS-84 的转换，正向偏移反推

def gcj2wgs(lat, lon):  
    g_lat, g_lon = wgs2gcj(lat, lon)  
    d_lat = g_lat - lat  
    d_lon = g_lon - lon  
    return lat - d_lat, lon - d_lon

def gcj2wgs(lat, lon):  
    g_lat, g_lon = wgs2gcj(lat, lon)  
    d_lat = g_lat - lat  
    d_lon = g_lon - lon  
    return lat - d_lat, lon - d_lon