GPS经纬度数据转换到以米单位的平面坐标系

//笛卡尔坐标系
typedef struct tagCRDCARTESIAN{
double x;
double y;
double z;
}CRDCARTESIAN,*PCRDCARTESIAN;
//typedef CRDCARTESIAN *PCRDCARTESIAN;
//大地坐标系
typedef struct tagCRDGEODETIC{
double longitude; //经度
double latitude;  //纬度 
double height;    //大地高,可设为0
}CRDGEODETIC;
typedef CRDGEODETIC *PCRDGEODETIC;

void CoordCovert::GeodeticToCartesian (PCRDCARTESIAN pcc, PCRDGEODETIC pcg,
double dSemiMajorAxis, double dFlattening)
{
    double B;    //纬度度数
    double L;    //经度度数
    double L0;    //中央经线度数
    double l;    //L-L0
    double t;    //tanB
    double m;    //ltanB
    double N;    //卯酉圈曲率半径 
    double q2;
    double x;    //高斯平面纵坐标
    double y;    //高斯平面横坐标
    double s;    //赤道至纬度B的经线弧长
    double f;    //参考椭球体扁率
    double e2;    //椭球第一偏心率
    double a;    //参考椭球体长半轴
    //double b;    //参考椭球体短半轴
    double a1;
    double a2;
    double a3;
    double a4;
    double b1;
    double b2;
    double b3;
    double b4;
    double c0;
    double c1;
    double c2;
    double c3;
    int Datum=84;    //投影基准面类型：北京54基准面为54，西安80基准面为80，WGS84基准面为84
    int prjno=0;    //投影带号
    int zonewide=3;    
    double IPI=0.0174532925199433333333;    //3.1415926535898/180.0
    B=pcg->latitude ; //纬度
    L=pcg->longitude ; //经度
    if (zonewide==6) 
    {
         prjno=(int)(L/zonewide)+1;
         L0=prjno*zonewide-3;
    }
    else
    {
        prjno=(int)((L-1.5)/3)+1;
        L0=prjno*3;
    }
    
    if(Datum==54)
    {
         a=6378245;
         f=1/298.3;
    }    
    else if(Datum==84)
    {
        a=6378137;
        f=1/298.257223563;
    }
    L0=L0*IPI;
    L=L*IPI;
    B=B*IPI;
    e2=2*f-f*f;//(a*a-b*b)/(a*a);
    l=L-L0;
    t=tan(B);
    m=l * cos(B);
    N=a/sqrt(1-e2* sin(B) * sin(B));
    q2=e2/(1-e2)* cos(B)* cos(B);
    a1=1+(double)3/4*e2+(double)45/64*e2*e2+(double)175/256*e2*e2*e2+(double)11025/16384*e2*e2*e2*e2+(double)43659/65536*e2*e2*e2*e2*e2;
    a2=(double)3/4*e2+(double)15/16*e2*e2+(double)525/512*e2*e2*e2+(double)2205/2048*e2*e2*e2*e2+(double)72765/65536*e2*e2*e2*e2*e2;
    a3=(double)15/64*e2*e2+(double)105/256*e2*e2*e2+(double)2205/4096*e2*e2*e2*e2+(double)10359/16384*e2*e2*e2*e2*e2;
    a4=(double)35/512*e2*e2*e2+(double)315/2048*e2*e2*e2*e2+(double)31185/13072*e2*e2*e2*e2*e2;
    b1=a1*a*(1-e2);
    b2=(double)-1/2*a2*a*(1-e2);
    b3=(double)1/4*a3*a*(1-e2);
    b4=(double)-1/6*a4*a*(1-e2);
    c0=b1;
    c1=2*b2+4*b3+6*b4;
    c2=-(8*b3+32*b4);
    c3=32*b4;
    s=c0*B+cos(B)*(c1*sin(B)+c2*sin(B)*sin(B)*sin(B)+c3*sin(B)*sin(B)*sin(B)*sin(B)*sin(B));
    x=s+(double)1/2*N*t*m*m+(double)1/24*(5-t*t+9*q2+4*q2*q2)*N*t*m*m*m*m+(double)1/720*(61-58*t*t+t*t*t*t)*N*t*m*m*m*m*m*m;
    y=N*m+(double)1/6*(1-t*t+q2)*N*m*m*m+(double)1/120*(5-18*t*t+t*t*t*t-14*q2-58*q2*t*t)*N*m*m*m*m*m;
    y=y+1000000*prjno+500000;
    pcc->x=x;
    pcc->y=y-38000000;
    pcc->z=0;
}