设计坐标系统类，命名为CoordSys。成员变量包含坐标系统的参考椭球 参数。该参数在构造函数中进行初始化。成员函数包含坐标转换功能函数，具 备XYZ2BLH，BLH2XYZ，XYZ2ENU三个函数。

以下是CoordSys类的代码实现：

#include <cmath>

class CoordSys {
private:
    double a; // 参考椭球长半轴
    double b; // 参考椭球短半轴
    double e2; // 第一偏心率平方

public:
    CoordSys(double a, double f) { // 构造函数，传入参考椭球长半轴和扁率f
        this->a = a;
        this->b = a * (1.0 - f);
        this->e2 = (a * a - b * b) / (a * a);
    }

    // XYZ转BLH
    void XYZ2BLH(double X, double Y, double Z, double& B, double& L, double& H) {
        double p = sqrt(X * X + Y * Y);
        double theta = atan2(Z * a, p * b);
        B = atan2(Z + e2 * b * pow(sin(theta), 3), p - e2 * a * pow(cos(theta), 3));
        L = atan2(Y, X);
        double N = a / sqrt(1 - e2 * pow(sin(B), 2));
        H = p / cos(B) - N;
    }

    // BLH转XYZ
    void BLH2XYZ(double B, double L, double H, double& X, double& Y, double& Z) {
        double N = a / sqrt(1 - e2 * pow(sin(B), 2));
        X = (N + H) * cos(B) * cos(L);
        Y = (N + H) * cos(B) * sin(L);
        Z = (N * (1 - e2) + H) * sin(B);
    }

    // XYZ转ENU
    void XYZ2ENU(double X, double Y, double Z, double B0, double L0, double& E, double& N, double& U) {
        double sinB = sin(B0);
        double cosB = cos(B0);
        double sinL = sin(L0);
        double cosL = cos(L0);
        double dx = -X * sinL + Y * cosL;
        double dy = -X * sinB * cosL - Y * sinB * sinL + Z * cosB;
        double dz = X * cosB * cosL + Y * cosB * sinL + Z * sinB;
        E = dx;
        N = dy;
        U = dz;
    }
};

使用示例：

#include <iostream>
#include "CoordSys.h"

int main() {
    CoordSys coordSys(6378137.0, 1.0 / 298.257223563); // WGS84参考椭球

    double X = 5000000.0;
    double Y = 400000.0;
    double Z = 1000000.0;
    double B, L, H;
    coordSys.XYZ2BLH(X, Y, Z, B, L, H);
    std::cout << "BLH: " << B << ", " << L << ", " << H << std::endl;

    double X2, Y2, Z2;
    coordSys.BLH2XYZ(B, L, H, X2, Y2, Z2);
    std::cout << "XYZ: " << X2 << ", " << Y2 << ", " << Z2 << std::endl;

    double E, N, U;
    coordSys.XYZ2ENU(X, Y, Z, B, L, E, N, U);
    std::cout << "ENU: " << E << ", " << N << ", " << U << std::endl;

    return 0;
}