用时域物理光学算法计算已知STL模型的RCS，需要C++代码

以下是使用时域物理光学算法计算已知STL模型的RCS的C++代码示例：

#include <iostream>
#include <fstream>
#include <string>
#include <vector>
#include <cmath>

using namespace std;

struct Vector3d {
    double x, y, z;

    Vector3d() : x(0), y(0), z(0) {}
    Vector3d(double x, double y, double z) : x(x), y(y), z(z) {}

    Vector3d operator+(const Vector3d& other) const {
        return Vector3d(x + other.x, y + other.y, z + other.z);
    }

    Vector3d operator-(const Vector3d& other) const {
        return Vector3d(x - other.x, y - other.y, z - other.z);
    }

    Vector3d operator*(double scalar) const {
        return Vector3d(x * scalar, y * scalar, z * scalar);
    }

    Vector3d cross(const Vector3d& other) const {
        return Vector3d(y * other.z - z * other.y,
                        z * other.x - x * other.z,
                        x * other.y - y * other.x);
    }

    double dot(const Vector3d& other) const {
        return x * other.x + y * other.y + z * other.z;
    }

    double magnitude() const {
        return sqrt(x * x + y * y + z * z);
    }

    Vector3d normalize() const {
        double mag = magnitude();
        return Vector3d(x / mag, y / mag, z / mag);
    }
};

struct Triangle {
    Vector3d v1, v2, v3;
    Vector3d normal;
    double area;

    Triangle() : area(0) {}

    Triangle(const Vector3d& v1, const Vector3d& v2, const Vector3d& v3) :
        v1(v1), v2(v2), v3(v3), area(0) {
        Vector3d e1 = v2 - v1;
        Vector3d e2 = v3 - v1;
        normal = e1.cross(e2).normalize();
        area = e1.cross(e2).magnitude() / 2;
    }
};

struct Ray {
    Vector3d origin, direction;

    Ray(const Vector3d& origin, const Vector3d& direction) :
        origin(origin), direction(direction.normalize()) {}
};

class Model {
public:
    Model(const string& filename) {
        ifstream ifs(filename);
        if (!ifs) {
            cerr << "Error: failed to open file " << filename << endl;
            return;
        }

        string line;
        while (getline(ifs, line)) {
            if (line.substr(0, 6) == "facet ") {
                Vector3d v1, v2, v3;
                while (getline(ifs, line)) {
                    if (line.substr(0, 14) == "    vertex ") {
                        double x, y, z;
                        sscanf(line.c_str() + 12, "%lf %lf %lf", &x, &y, &z);
                        Vector3d v(x, y, z);
                        if (!v1.x && !v1.y && !v1.z) {
                            v1 = v;
                        } else if (!v2.x && !v2.y && !v2.z) {
                            v2 = v;
                        } else if (!v3.x && !v3.y && !v3.z) {
                            v3 = v;
                            triangles.push_back(Triangle(v1, v2, v3));
                            break;
                        }
                    }
                }
            }
        }
    }

    double getRCS(const Ray& incident_ray, double frequency) const {
        double wavelength = 3e8 / frequency;
        double k = 2 * M_PI / wavelength;
        Vector3d E0(1, 0, 0);
        Vector3d H0(0, 1, 0);
        double eta = 120 * M_PI;

        Vector3d Ei = E0;
        Vector3d Hi = H0.cross(incident_ray.direction).normalize();

        double total_rcs = 0;
        for (auto& triangle : triangles) {
            Vector3d n = triangle.normal;
            double A = triangle.area;
            Vector3d v1 = triangle.v1;
            Vector3d v2 = triangle.v2;
            Vector3d v3 = triangle.v3;

            Vector3d E1 = Ei * exp(-1i * k * incident_ray.direction.dot(v1));
            Vector3d H1 = Hi * exp(-1i * k * incident_ray.direction.dot(v1));
            Vector3d E2 = Ei * exp(-1i * k * incident_ray.direction.dot(v2));
            Vector3d H2 = Hi * exp(-1i * k * incident_ray.direction.dot(v2));
            Vector3d E3 = Ei * exp(-1i * k * incident_ray.direction.dot(v3));
            Vector3d H3 = Hi * exp(-1i * k * incident_ray.direction.dot(v3));

            Vector3d E = E1 + E2 + E3;
            Vector3d H = H1 + H2 + H3;

            double gamma = eta * (E.cross(n)).magnitude() / H.magnitude();
            double rcs = pow(gamma * A / (4 * M_PI * wavelength), 2);
            total_rcs += rcs;
        }

        return total_rcs;
    }

private:
    vector<Triangle> triangles;
};

int main() {
    Model model("example.stl");
    Ray incident_ray(Vector3d(0, 0, -1), Vector3d(0, 0, 1));
    double frequency = 1e9;
    double rcs = model.getRCS(incident_ray, frequency);
    cout << "RCS: " << rcs << endl;
    return 0;
}

该代码中使用了STL文件格式读取模型，计算RCS时使用了电场和磁场，以及散射系数和反射系数的计算公式。需要注意的是，该代码仅供参考，实际应用中需要根据具体情况进行调整和优化。