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: 衛星橢球座標投影到平面地圖座標系的投影因子。
        var ee = 0.00669342162296594323; //  ee: 橢球的偏心率。
        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-02
    gcj_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-84
    gcj_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 exactly
    gcj_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-09
    bd_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-02
    bd_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 -> x
    mercator_encrypt : function(wgsLat, wgsLon) {
        var x = wgsLon * 20037508.34 / 180.;
        var y = Math.log(Math.tan((90. + wgsLat) * this.PI / 360.)) / (this.PI / 180.);
        y = y * 20037508.34 / 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 -> x
    mercator_decrypt : function(mercatorLat, mercatorLon) {
        var x = mercatorLon / 20037508.34 * 180.;
        var y = mercatorLat / 20037508.34 * 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) > 20037508.3427892) || (Math.abs(mercatorLat) > 20037508.3427892))
            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 distance
    distance : 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;
    }
};