高斯坐标转换经纬度

// 高斯坐标转经纬度
const Gauss_to_LogLat = (Y,X) => {
    let lat, lon
    Y-=500000;
    let result = new Array(2);
    let iPI = 0.0174532925199433; //pi/180
    let a = 6378137.0; //长半轴 m
    let b = 6356752.31414; //短半轴 m
    let f = 1/298.257222101;//扁率 a-b/a
    let e = 0.0818191910428; //第一偏心率 Math.sqrt(5)
    let L0 = 114; //中央子午线的经线值
    let ee = Math.sqrt(a*a-b*b)/b; //第二偏心率
    let bf = 0; //底点纬度
    let a0 = 1+(3*e*e/4) + (45*e*e*e*e/64) + (175*e*e*e*e*e*e/256) + (11025*e*e*e*e*e*e*e*e/16384) + (43659*e*e*e*e*e*e*e*e*e*e/65536);
    let b0 = X/(a*(1-e*e)*a0);
    let c1 = 3*e*e/8 +3*e*e*e*e/16 + 213*e*e*e*e*e*e/2048 + 255*e*e*e*e*e*e*e*e/4096;
    let c2 = 21*e*e*e*e/256 + 21*e*e*e*e*e*e/256 + 533*e*e*e*e*e*e*e*e/8192;
    let c3 = 151*e*e*e*e*e*e*e*e/6144 + 151*e*e*e*e*e*e*e*e/4096;
    let c4 = 1097*e*e*e*e*e*e*e*e/131072;
    bf = b0 + c1*Math.sin(2*b0) + c2*Math.sin(4*b0) +c3*Math.sin(6*b0) + c4*Math.sin(8*b0); // bf =b0+c1*sin2b0 + c2*sin4b0 + c3*sin6b0 +c4*sin8b0 +...
    let tf = Math.tan(bf);
    let n2 = ee*ee*Math.cos(bf)*Math.cos(bf); //第二偏心率平方成bf余弦平方
    let c = a*a/b;
    let v = Math.sqrt(1+ ee*ee*Math.cos(bf)*Math.cos(bf));
    let mf = c/(v*v*v); //子午圈半径
    let nf = c/v;//卯酉圈半径

    //纬度计算
    lat = bf-(tf/(2*mf)*Y)*(Y/nf) * (1-1/12*(5+3*tf*tf+n2-9*n2*tf*tf)*(Y*Y/(nf*nf))+1/360*(61+90*tf*tf+45*tf*tf*tf*tf)*(Y*Y*Y*Y/(nf*nf*nf*nf)));
    //经度偏差
    lon = 1/(nf*Math.cos(bf))*Y -(1/(6*nf*nf*nf*Math.cos(bf)))*(1+2*tf*tf +n2)*Y*Y*Y + (1/(120*nf*nf*nf*nf*nf*Math.cos(bf)))*(5+28*tf*tf+24*tf*tf*tf*tf)*Y*Y*Y*Y*Y;
    result[0] = L0 + lon / iPI;
    result[1] = lat / iPI;
    return result
}