在互联网上可以免费使用的在线地图有很多种，包括google map,百度地图，高德地图，腾讯地图，天地图等等。各种地图并没有使用同样的坐标系，这样就导致更换地图API时，使用同样的经纬度在不同的地图底图上，会存在偏差，这种变差还比较大。在GPS定位技术以及在线地图普遍使用的今天，即使是极细微的偏差，也会造成使用上的极大不便。
下面将提供各类地图经纬度的转换方法，用JavaScript语言实现。
//转换常数var x_pi = 3.14159265358979324 * 3000.0 / 180.0;var pi = 3.14159265358979324;var a = 6378245.0;var ee = 0.00669342162296594323;function transformLon(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 * 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;};function transformLat(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 * 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;}function outOfChina(lat, lon) {if (lon < 72.004 || lon > 137.8347)return true;if (lat < 0.8293 || lat > 55.8271)return true;return false;}/* * WGS-84：是国际标准，GPS坐标（Google Earth使用、或者GPS模块、天地图）* 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*//*** wgLat 纬度* wgLon 经度* WGS-84 到 GCJ-02 的转换（即 GPS 加偏）* */function wgs_gcj_encrypts(wgLat, wgLon) {var point={};if (outOfChina(wgLat, wgLon)) {point.lat=wgLat;point.lng=wgLon;return point;}var dLat = transformLat(wgLon - 105.0, wgLat - 35.0);var dLon = transformLon(wgLon - 105.0, wgLat - 35.0);var radLat = wgLat / 180.0 * 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) * pi);dLon = (dLon * 180.0) / (a / sqrtMagic * Math.cos(radLat) * pi);var lat = wgLat + dLat;var lon = wgLon + dLon;point.lat=lat;point.lon=lon;return point;};/*** wgLat 纬度* wgLon 经度* BD-09转换GCJ-02* 百度转google* */function bd_google_encrypt(bd_lat, bd_lon){var point={};var x = bd_lon - 0.0065;var y = 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 gg_lon = z * Math.cos(theta); var gg_lat = z * Math.sin(theta); point.lat=gg_lat;point.lon=gg_lon;return point;};/*** gg_lat 纬度* gg_lon 经度* GCJ-02转换BD-09* Google地图经纬度转百度地图经纬度* */function google_bd_encrypt(gg_lat, gg_lon){var point={};var x = gg_lon;var y = 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.lat=bd_lat;point.lon=bd_lon;return point;};
