一、地图坐标系解释
在进行地图开发过程中，我们一般能接触到以下三种类型的地图坐标系：
WGS－84原始坐标系，一般用国际GPS纪录仪记录下来的经纬度，通过GPS定位拿到的原始经纬度，Google和高德地图定位的的经纬度（国外）都是基于WGS－84坐标系的。但是在国内是不允许直接用WGS84坐标系标注的，必须经过加密后才能使用。
GCJ－02坐标系，又名“火星坐标系”，是我国国测局独创的坐标体系，由WGS－84加密而成，在国内，必须至少使用GCJ－02坐标系，或者使用在GCJ－02加密后再进行加密的坐标系，如百度坐标系。高德和Google在国内都是使用GCJ－02坐标系，可以说，GCJ－02是国内最广泛使用的坐标系。
百度坐标系：bd-09，百度坐标系是在GCJ－02坐标系的基础上再次加密偏移后形成的坐标系，只适用于百度地图。(目前百度API提供了从其它坐标系转换为百度坐标系的API，但却没有从百度坐标系转为其他坐标系的API)。
二、坐标系转换（C#版本）
以下为WGS-84、GCJ02、BD-09的坐标系之间相互转换的方法：
/// <summary>/// 圆周率/// </summary>private const double PI = 3.14159265358979324;private const double X_PI = 3.14159265358979324 * 3000.0 / 180.0;private const double A = 6378245.0;private const double EE = 0.00669342162296594323;private const double LON_BOUNDARY_MIN = 72.004;private const double LAT_BOUNDARY_MIN = 0.8293;private const double LON_BOUNDARY_MAX = 137.8347;private const double LAT_BOUNDARY_MAX = 55.8271;/// <summary>/// 是否中国境内坐标/// </summary>/// <param name="gpsLat"></param>/// <param name="gpsLng"></param>/// <returns></returns>private static bool OutOfChina(double gpsLat, double gpsLng){if (gpsLng < LON_BOUNDARY_MIN || gpsLng > LON_BOUNDARY_MAX){return true;}if (gpsLat < LAT_BOUNDARY_MIN || gpsLat > LAT_BOUNDARY_MAX){return true;}return false;}#region WGS坐标系与GCJ02坐标系互转/// <summary>/// WGS84坐标系转GCJ02坐标系/// </summary>/// <param name="wgsLat">WGS坐标，纬度</param>/// <param name="wgsLng">WGS坐标，经度</param>/// <param name="gcjLat">GCJ02坐标，纬度</param>/// <param name="gcjLng">GCJ02坐标，经度</param>public static void WGS84_to_GCJ02(double wgsLat, double wgsLng, out double gcjLat, out double gcjLng){if (OutOfChina(wgsLat, wgsLng)){gcjLat = wgsLat;gcjLng = wgsLng;}else{double dLat = TransformLat(wgsLng - 105.0, wgsLat - 35.0);double dLon = TransformLon(wgsLng - 105.0, wgsLat - 35.0);double radLat = wgsLat / 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);gcjLat = wgsLat + dLat;gcjLng = wgsLng + dLon;}}public static void GCJ02_to_WGS84(double gcjLat, double gcjLng, out double wgsLat, out double wgsLng){WGS84_to_GCJ02(gcjLat, gcjLng, out wgsLat, out wgsLng);wgsLng = gcjLng * 2 - wgsLng;wgsLat = gcjLat * 2 - wgsLat;}private 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;}private 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;}#endregion#region 火星坐标系 (GCJ-02) 与百度坐标系 (BD-09) 的互转public static void GCJ02_to_Bd09(double gcjLat, double gcjLng, out double bdLat, out double bdLng){double z = Math.Sqrt(gcjLng * gcjLng + gcjLat * gcjLat) + 0.00002 * Math.Sin(gcjLat * PI);double theta = Math.Atan2(gcjLat, gcjLng) + 0.000003 * Math.Cos(gcjLng * PI);bdLng = z * Math.Cos(theta) + 0.0065;bdLat = z * Math.Sin(theta) + 0.006;}public static void BD09_to_GCJ02(double bdLat, double bdLng, out double gcjLat, out double gcjLng){double x = bdLng - 0.0065, y = bdLat - 0.006;double z = Math.Sqrt(x * x + y * y) - 0.00002 * Math.Sin(y * PI);double theta = Math.Atan2(y, x) - 0.000003 * Math.Cos(x * PI);gcjLng = z * Math.Cos(theta);gcjLat = z * Math.Sin(theta);}#endregion
三、QT/C++版本的坐标转换
创建头文件，QGCTransform.h：
#ifndef QGCTRANSFORM_H#define QGCTRANSFORM_Hstruct gps_position_t {int32_t lat; /*< Latitude, expressed as degrees * 1E7*/int32_t lon; /*< Longitude, expressed as degrees * 1E7*/double lat_f;double lon_f;};class QGCTransform{public:QGCTransform();/*WGS-84 to GCJ-02*/double PI;double a;double ee;gps_position_t gps_t;void Transform();void Transform(double lat, double lon);private:bool OutOfChina(double lat, double lon);double TransformLat(double x, double y);double TransformLon(double x, double y);};#endif // QGCTRANSFORM_H
创建源文件，QGCTransform.cpp，转换后的GPS经纬度存储在结构体“gps_t”中，代码如下：
#include "QGCTransform.h"#include <QtMath>QGCTransform::QGCTransform(){PI = 3.14159265358979324;a = 6378245.0;ee = 0.00669342162296594323;}/*WGS-84 to GCJ-02*/bool QGCTransform::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;}double QGCTransform::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 * qSqrt(qAbs(x));ret += (20.0 * qSin(6.0 * x * PI) + 20.0 * qSin(2.0 * x * PI)) * 2.0 / 3.0;ret += (20.0 * qSin(y * PI) + 40.0 * qSin(y / 3.0 * PI)) * 2.0 / 3.0;ret += (160.0 * qSin(y / 12.0 * PI) + 320 * qSin(y * PI / 30.0)) * 2.0 / 3.0;return ret;}double QGCTransform::TransformLon(double x, double y){double ret = 300.0 + x + 2.0 * y + 0.1 * x * x + 0.1 * x * y + 0.1 * qSqrt(qAbs(x));ret += (20.0 * qSin(6.0 * x * PI) + 20.0 * qSin(2.0 * x * PI)) * 2.0 / 3.0;ret += (20.0 * qSin(x * PI) + 40.0 * qSin(x / 3.0 * PI)) * 2.0 / 3.0;ret += (150.0 * qSin(x / 12.0 * PI) + 300.0 * qSin(x / 30.0 * PI)) * 2.0 / 3.0;return ret;}void QGCTransform::Transform(){double lat_s=gps_t.lat * 1E-7;double lon_s=gps_t.lon * 1E-7;Transform(lat_s, lon_s);}void QGCTransform::Transform(double lat_s, double lon_s){gps_t.lat_f = lat_s;gps_t.lon_f = lon_s;gps_t.lat = lat_s * 1E7;gps_t.lon = lon_s * 1E7;if (OutOfChina(lat_s, lon_s )){return;}double dLat = TransformLat(lon_s - 105.0, lat_s - 35.0);double dLon = TransformLon(lon_s - 105.0, lat_s - 35.0);double radLat = lat_s / 180.0 * PI;double magic = qSin(radLat);magic = 1 - ee * magic * magic;double sqrtMagic = qSqrt(magic);dLat = (dLat * 180.0) / ((a * (1 - ee)) / (magic * sqrtMagic) * PI);dLon = (dLon * 180.0) / (a / sqrtMagic * qCos(radLat) * PI);gps_t.lat = (lat_s + dLat) * 1E7;gps_t.lon = (lon_s + dLon) * 1E7;gps_t.lat_f = lat_s + dLat;gps_t.lon_f = lon_s + dLon;}
引用：
1、高德，百度，Google地图定位偏移以及坐标系转换
