写一段将ply点云文件中的各个点按kruskal最小生成树的顺序连成可视化线段的C++代码

以下是将ply点云文件中的各个点按kruskal最小生成树的顺序连成可视化线段的C++代码：

#include <iostream>
#include <fstream>
#include <vector>
#include <algorithm>

#include <pcl/point_types.h>
#include <pcl/io/ply_io.h>
#include <pcl/visualization/pcl_visualizer.h>

struct Edge {
    int src;
    int dst;
    double weight;
};

bool cmp(const Edge& e1, const Edge& e2) {
    return e1.weight < e2.weight;
}

int find(int x, std::vector<int>& parent) {
    if (parent[x] == x) {
        return x;
    }
    return parent[x] = find(parent[x], parent);
}

void Union(int x, int y, std::vector<int>& parent) {
    int px = find(x, parent);
    int py = find(y, parent);
    parent[py] = px;
}

std::vector<Edge> kruskal(std::vector<Edge>& edges, int n) {
    std::vector<int> parent(n);
    for (int i = 0; i < n; ++i) {
        parent[i] = i;
    }

    std::sort(edges.begin(), edges.end(), cmp);

    std::vector<Edge> mst;
    for (int i = 0; i < edges.size(); ++i) {
        int src = edges[i].src;
        int dst = edges[i].dst;
        if (find(src, parent) != find(dst, parent)) {
            Union(src, dst, parent);
            mst.push_back(edges[i]);
        }
    }

    return mst;
}

int main(int argc, char** argv) {
    if (argc < 2) {
        std::cerr << "Please provide input file." << std::endl;
        return -1;
    }

    pcl::PointCloud<pcl::PointXYZ>::Ptr cloud(new pcl::PointCloud<pcl::PointXYZ>);
    pcl::io::loadPLYFile(argv[1], *cloud);

    int n = cloud->size();
    std::vector<Edge> edges(n * (n - 1) / 2);
    int idx = 0;
    for (int i = 0; i < n; ++i) {
        for (int j = i + 1; j < n; ++j) {
            double dist = std::sqrt(std::pow(cloud->points[i].x - cloud->points[j].x, 2) +
                                    std::pow(cloud->points[i].y - cloud->points[j].y, 2) +
                                    std::pow(cloud->points[i].z - cloud->points[j].z, 2));
            edges[idx++] = {i, j, dist};
        }
    }

    std::vector<Edge> mst = kruskal(edges, n);

    pcl::visualization::PCLVisualizer viewer("Minimum Spanning Tree");
    viewer.setBackgroundColor(0, 0, 0);
    viewer.addPointCloud<pcl::PointXYZ>(cloud, "cloud");
    viewer.setPointCloudRenderingProperties(pcl::visualization::PCL_VISUALIZER_POINT_SIZE, 3, "cloud");

    for (int i = 0; i < mst.size(); ++i) {
        pcl::PointXYZ p1 = cloud->points[mst[i].src];
        pcl::PointXYZ p2 = cloud->points[mst[i].dst];
        std::string line_id = "line_" + std::to_string(i);
        viewer.addLine(p1, p2, 1.0, 0.0, 0.0, line_id);
    }

    viewer.spin();

    return 0;
}

该程序的实现步骤为：

1. 读取ply点云文件；
2. 计算任意两个点之间的距离，构建完全图，即所有点之间都有一条边；
3. 对边按权值从小到大排序；
4. 依次取最小的边，如果这条边的两个顶点不在同一个连通块中，则将这条边加入最小生成树中，并将这两个顶点合并到同一个连通块中；
5. 将最小生成树的边可视化为线段并显示在窗口中。

注：该程序使用了PCL库进行读取ply文件和可视化，因此需要安装PCL库