经纬度偏移转换

在进行地图开发过程中，一般能接触到以下三种类型的地图坐标系：

1.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；

2.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；

3.百度坐标系: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)

using system;
using system.collections.generic;
using system.linq;
using system.web;

namespace extensions
{
    public class gpsextension
    {
        public static double pi = 3.1415926535897932384626;
        public static double x_pi = 3.14159265358979324 * 3000.0 / 180.0;
        public static double a = 6378245.0;
        public static double ee = 0.00669342162296594323;

        public 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;
        }

        public 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;
        }
        public static double[] transform(double lat, double lon)
        {
            if (outofchina(lat, lon))
            {
                return new double[] { lat, lon };
            }
            double dlat = transformlat(lon - 105.0, lat - 35.0);
            double dlon = transformlon(lon - 105.0, lat - 35.0);
            double radlat = lat / 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);
            double mglat = lat + dlat;
            double mglon = lon + dlon;
            return new double[] { mglat, mglon };
        }
        public 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;
        }
        /** 
         * 84 to 火星坐标系 (gcj-02) world geodetic system ==> mars geodetic system 
         * 
         * @param lat 
         * @param lon 
         * @return 
         */
        public static double[] gps84_to_gcj02(double lat, double lon)
        {
            if (outofchina(lat, lon))
            {
                return new double[] { lat, lon };
            }
            double dlat = transformlat(lon - 105.0, lat - 35.0);
            double dlon = transformlon(lon - 105.0, lat - 35.0);
            double radlat = lat / 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);
            double mglat = lat + dlat;
            double mglon = lon + dlon;
            return new double[] { mglat, mglon };
        }


        /// <summary>
        /// 火星坐标系 (gcj-02) to 84 * * @param lon * @param lat * @return 
        /// </summary>
        /// <param name="lat"></param>
        /// <param name="lon"></param>
        /// <returns></returns>
        public static double[] gcj02_to_gps84(double lat, double lon)
        {
            double[] gps = transform(lat, lon);
            double lontitude = lon * 2 - gps[1];
            double latitude = lat * 2 - gps[0];
            return new double[] { latitude, lontitude };
        }
        /** 
         * 火星坐标系 (gcj-02) 与百度坐标系 (bd-09) 的转换算法 将 gcj-02 坐标转换成 bd-09 坐标 
         * 
         * @param lat 
         * @param lon 
         */
        public static double[] gcj02_to_bd09(double lat, double lon)
        {
            double x = lon, y = lat;
            double z = math.sqrt(x * x + y * y) + 0.00002 * math.sin(y * x_pi);
            double theta = math.atan2(y, x) + 0.000003 * math.cos(x * x_pi);
            double templon = z * math.cos(theta) + 0.0065;
            double templat = z * math.sin(theta) + 0.006;
            double[] gps = { templat, templon };
            return gps;
        }

        /** 
         * * 火星坐标系 (gcj-02) 与百度坐标系 (bd-09) 的转换算法 * * 将 bd-09 坐标转换成gcj-02 坐标 * * @param 
         * bd_lat * @param bd_lon * @return 
         */
        public static double[] bd09_to_gcj02(double lat, double lon)
        {
            double x = lon - 0.0065, y = lat - 0.006;
            double z = math.sqrt(x * x + y * y) - 0.00002 * math.sin(y * x_pi);
            double theta = math.atan2(y, x) - 0.000003 * math.cos(x * x_pi);
            double templon = z * math.cos(theta);
            double templat = z * math.sin(theta);
            double[] gps = { templat, templon };
            return gps;
        }

        /**将gps84转为bd09 
         * @param lat 
         * @param lon 
         * @return 
         */
        public static double[] gps84_to_bd09(double lat, double lon)
        {
            double[] gcj02 = gps84_to_gcj02(lat, lon);
            double[] bd09 = gcj02_to_bd09(gcj02[0], gcj02[1]);
            return bd09;
        }
        public static double[] bd09_to_gps84(double lat, double lon)
        {
            double[] gcj02 = bd09_to_gcj02(lat, lon);
            double[] gps84 = gcj02_to_gps84(gcj02[0], gcj02[1]);
            //保留小数点后六位  
            gps84[0] = retain6(gps84[0]);
            gps84[1] = retain6(gps84[1]);
            return gps84;
        }

        /**保留小数点后六位 
         * @param num 
         * @return 
         */
        private static double retain6(double num)
        {
            string result = string.format("%.6f", num);
            return convert.todouble(result);
        }
    }
}