问题
今天用react-native原生GPS拿到得定位信息,如图：
之前高德地图取到的定位数据为（显示带有longtitude,latitude===的log）准确的
121.518828125，31.19265407986111
用原生GPS获取的数据为（显示为GPS++++++±====log）
121.514452，31.194733
发现只有小数后几位的区别，一直傻了吧唧的以为定位误差，看着也就差了几百米，其实是坐标系没有转换存在的误差。
本质上是WGS-84与GCJ-02之间为转换导致的误差
## 现成的转换代码之javascript版本：
WGS-84：是国际标准，GPS坐标（Google Earth使用、或者GPS模块）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//WGS-84 to GCJ-02GPS.gcj_encrypt();//GCJ-02 to WGS-84 粗略GPS.gcj_decrypt();//GCJ-02 to WGS-84 精确(二分极限法)// var threshold = 0.000000001; 目前设置的是精确到小数点后9位，这个值越小，越精确，但是javascript中，浮点运算本身就不太精确，九位在GPS里也偏差不大了GSP.gcj_decrypt_exact();//GCJ-02 to BD-09GPS.bd_encrypt();//BD-09 to GCJ-02GPS.bd_decrypt();//求距离GPS.distance();示例：document.write("GPS: 39.933676862706776,116.35608315379092<br />");var arr2 = GPS.gcj_encrypt(39.933676862706776, 116.35608315379092);document.write("中国:" + arr2['lat']+","+arr2['lon']+'<br />');var arr3 = GPS.gcj_decrypt_exact(arr2['lat'], arr2['lon']);document.write('逆算:' + arr3['lat']+","+arr3['lon']+' 需要和第一行相似（目前是小数点后9位相等）');JavaScript代码 var GPS = {PI : 3.14159265358979324,x_pi : 3.14159265358979324 * 3000.0 / 180.0,delta : function (lat, lon) {// Krasovsky 1940//// a = 6378245.0, 1/f = 298.3// b = a * (1 - f)// ee = (a^2 - b^2) / a^2;var a = 6378245.0; // a: 卫星椭球坐标投影到平面地图坐标系的投影因子。var ee = 0.00669342162296594323; // ee: 椭球的偏心率。var dLat = this.transformLat(lon - 105.0, lat - 35.0);var dLon = this.transformLon(lon - 105.0, lat - 35.0);var radLat = lat / 180.0 * this.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) * this.PI);dLon = (dLon * 180.0) / (a / sqrtMagic * Math.cos(radLat) * this.PI);return {'lat': dLat, 'lon': dLon};},//WGS-84 to GCJ-02gcj_encrypt : function (wgsLat, wgsLon) {if (this.outOfChina(wgsLat, wgsLon))return {'lat': wgsLat, 'lon': wgsLon};var d = this.delta(wgsLat, wgsLon);return {'lat' : wgsLat + d.lat,'lon' : wgsLon + d.lon};},//GCJ-02 to WGS-84gcj_decrypt : function (gcjLat, gcjLon) {if (this.outOfChina(gcjLat, gcjLon))return {'lat': gcjLat, 'lon': gcjLon};var d = this.delta(gcjLat, gcjLon);return {'lat': gcjLat - d.lat, 'lon': gcjLon - d.lon};},//GCJ-02 to WGS-84 exactlygcj_decrypt_exact : function (gcjLat, gcjLon) {var initDelta = 0.01;var threshold = 0.000000001;var dLat = initDelta, dLon = initDelta;var mLat = gcjLat - dLat, mLon = gcjLon - dLon;var pLat = gcjLat + dLat, pLon = gcjLon + dLon;var wgsLat, wgsLon, i = 0;while (1) {wgsLat = (mLat + pLat) / 2;wgsLon = (mLon + pLon) / 2;var tmp = this.gcj_encrypt(wgsLat, wgsLon)dLat = tmp.lat - gcjLat;dLon = tmp.lon - gcjLon;if ((Math.abs(dLat) < threshold) && (Math.abs(dLon) < threshold))break;if (dLat > 0) pLat = wgsLat; else mLat = wgsLat;if (dLon > 0) pLon = wgsLon; else mLon = wgsLon;if (++i > 10000) break;}//console.log(i);return {'lat': wgsLat, 'lon': wgsLon};},//GCJ-02 to BD-09bd_encrypt : function (gcjLat, gcjLon) {var x = gcjLon, y = gcjLat; var z = Math.sqrt(x * x + y * y) + 0.00002 * Math.sin(y * this.x_pi); var theta = Math.atan2(y, x) + 0.000003 * Math.cos(x * this.x_pi); bdLon = z * Math.cos(theta) + 0.0065; bdLat = z * Math.sin(theta) + 0.006; return {'lat' : bdLat,'lon' : bdLon};},//BD-09 to GCJ-02bd_decrypt : function (bdLat, bdLon) {var x = bdLon - 0.0065, y = bdLat - 0.006; var z = Math.sqrt(x * x + y * y) - 0.00002 * Math.sin(y * this.x_pi); var theta = Math.atan2(y, x) - 0.000003 * Math.cos(x * this.x_pi); var gcjLon = z * Math.cos(theta); var gcjLat = z * Math.sin(theta);return {'lat' : gcjLat, 'lon' : gcjLon};},//WGS-84 to Web mercator//mercatorLat -> y mercatorLon -> xmercator_encrypt : function(wgsLat, wgsLon) {var x = wgsLon * 7508.34 / 180.;var y = Math.log(Math.tan((90. + wgsLat) * this.PI / 360.)) / (this.PI / 180.);y = y * 7508.34 / 180.;return {'lat' : y, 'lon' : x};/*if ((Math.abs(wgsLon) > 180 || Math.abs(wgsLat) > 90))return null;var x = 6378137.0 * wgsLon * 0.017453292519943295;var a = wgsLat * 0.017453292519943295;var y = 3189068.5 * Math.log((1.0 + Math.sin(a)) / (1.0 - Math.sin(a)));return {'lat' : y, 'lon' : x};//*/},// Web mercator to WGS-84// mercatorLat -> y mercatorLon -> xmercator_decrypt : function(mercatorLat, mercatorLon) {var x = mercatorLon / 7508.34 * 180.;var y = mercatorLat / 7508.34 * 180.;y = 180 / this.PI * (2 * Math.atan(Math.exp(y * this.PI / 180.)) - this.PI / 2);return {'lat' : y, 'lon' : x};/*if (Math.abs(mercatorLon) < 180 && Math.abs(mercatorLat) < 90)return null;if ((Math.abs(mercatorLon) > 7508.3427892) || (Math.abs(mercatorLat) > 7508.3427892))return null;var a = mercatorLon / 6378137.0 * 57.295779513082323;var x = a - (Math.floor(((a + 180.0) / 360.0)) * 360.0);var y = (1.5707963267948966 - (2.0 * Math.atan(Math.exp((-1.0 * mercatorLat) / 6378137.0)))) * 57.295779513082323;return {'lat' : y, 'lon' : x};//*/},// two point's distancedistance : function (latA, lonA, latB, lonB) {var earthR = 6371000.;var x = Math.cos(latA * this.PI / 180.) * Math.cos(latB * this.PI / 180.) * Math.cos((lonA - lonB) * this.PI / 180);var y = Math.sin(latA * this.PI / 180.) * Math.sin(latB * this.PI / 180.);var s = x + y;if (s > 1) s = 1;if (s < -1) s = -1;var alpha = Math.acos(s);var distance = alpha * earthR;return distance;},outOfChina : function (lat, lon) {if (lon < 72.004 || lon > 137.8347)return true;if (lat < 0.8293 || lat > 55.8271)return true;return false;},transformLat : function (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 * this.PI) + 20.0 * Math.sin(2.0 * x * this.PI)) * 2.0 / 3.0;ret += (20.0 * Math.sin(y * this.PI) + 40.0 * Math.sin(y / 3.0 * this.PI)) * 2.0 / 3.0;ret += (160.0 * Math.sin(y / 12.0 * this.PI) + 320 * Math.sin(y * this.PI / 30.0)) * 2.0 / 3.0;return ret;},transformLon : function (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 * this.PI) + 20.0 * Math.sin(2.0 * x * this.PI)) * 2.0 / 3.0;ret += (20.0 * Math.sin(x * this.PI) + 40.0 * Math.sin(x / 3.0 * this.PI)) * 2.0 / 3.0;ret += (150.0 * Math.sin(x / 12.0 * this.PI) + 300.0 * Math.sin(x / 30.0 * this.PI)) * 2.0 / 3.0;return ret;}};
参考：
地图开发之百度、高德、GPS坐标坐标互转
