C语言实现 ransac多项式拟合算法

RANSAC（RANdom SAmple Consensus）是一种基于随机采样和一致性检验的算法，常用于拟合数据模型。下面是一个使用C语言实现RANSAC多项式拟合算法的示例代码：

#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <time.h>

#define MAX_ITERATIONS 1000
#define THRESHOLD 0.01

// 生成随机数
double rand_double(double min, double max) {
    double range = (max - min) + 1.0;
    return (double)(rand() / RAND_MAX) * range + min;
}

// 计算多项式函数值
double polyval(double *coeffs, int degree, double x) {
    double result = 0.0;
    for (int i = degree; i >= 0; i--) {
        result += coeffs[i] * pow(x, i);
    }
    return result;
}

// RANSAC多项式拟合算法
int ransac_polyfit(double *x, double *y, int n, int degree, double *best_coeffs) {
    int best_inliers = 0;
    int *inliers = (int *)malloc(n * sizeof(int));
    double *coeffs = (double *)malloc((degree + 1) * sizeof(double));
    srand(time(NULL));

    // 迭代多次
    for (int i = 0; i < MAX_ITERATIONS; i++) {
        // 随机选择一些点
        int idx1 = rand() % n;
        int idx2 = rand() % n;
        while (idx2 == idx1) {
            idx2 = rand() % n;
        }

        // 计算多项式系数
        double x1 = x[idx1];
        double x2 = x[idx2];
        double y1 = y[idx1];
        double y2 = y[idx2];
        coeffs[1] = (y2 - y1) / (x2 - x1);
        coeffs[0] = y1 - coeffs[1] * x1;

        // 计算内点
        int num_inliers = 0;
        for (int j = 0; j < n; j++) {
            double error = fabs(polyval(coeffs, degree, x[j]) - y[j]);
            if (error < THRESHOLD) {
                inliers[num_inliers++] = j;
            }
        }

        // 如果内点数量大于当前最优解，则更新最优解
        if (num_inliers > best_inliers) {
            best_inliers = num_inliers;
            for (int j = 0; j < degree + 1; j++) {
                best_coeffs[j] = coeffs[j];
            }
        }
    }

    free(inliers);
    free(coeffs);
    return best_inliers;
}

int main() {
    int n = 10; // 数据点数量
    double *x = (double *)malloc(n * sizeof(double));
    double *y = (double *)malloc(n * sizeof(double));
    double *coeffs = (double *)malloc(3 * sizeof(double));

    // 生成数据点
    for (int i = 0; i < n; i++) {
        x[i] = rand_double(0.0, 10.0);
        y[i] = 3.0 * x[i] * x[i] + 2.0 * x[i] + rand_double(-1.0, 1.0);
    }

    // 多项式拟合
    int num_inliers = ransac_polyfit(x, y, n, 2, coeffs);
    printf("Best fit: y = %.2lfx^2 + %.2lfx + %.2lf\n", coeffs[2], coeffs[1], coeffs[0]);
    printf("Number of inliers: %d\n", num_inliers);

    free(x);
    free(y);
    free(coeffs);
    return 0;
}

在上面的示例代码中，我们使用RANSAC算法拟合了一个二次多项式模型，并打印出了最优拟合结果和内点数量。你可以根据自己的需求修改代码中的参数和数据点，来实现你所需要的多项式拟合算法。