点云可视化

可视化（Visualization）是利用计算机图形学和图像处理技术，将数据转换成图形或图像在屏幕显示出来，并且进行交互处理的理论、方法和技术。

PCL中pcl_visualization库中提供了可视化相关的数据结构和组件，其主要是为了可视化其他模块算法处理后的结果，可直观的反馈给用户。其依赖于pcl_common、pcl_range_image、pcl_kdtree、pcl_IO模块以及VTK外部开源可视化库。下面给出2个常用的可视化类。

• pcl::visualization::PCLVisualizer

PCLVisualizer是PCL可视化3D点云的主要类。其内部实现了添加各种3D对象以及交互的实现等，比其他类实现的功能更齐全。

基础显示功能： 显示点云、网格、设置颜色、连线

#include <pcl/io/pcd_io.h>
#include <pcl/io/ply_io.h>
#include <pcl/point_types.h>
// 包含相关头文件
#include <pcl/visualization/pcl_visualizer.h>

typedef pcl::PointXYZ PointT;

int main()
{
    // 读取点云
    pcl::PointCloud<PointT>::Ptr cloud1(new pcl::PointCloud<PointT>);
    pcl::io::loadPCDFile("read1.pcd", *cloud1);

    pcl::PointCloud<PointT>::Ptr cloud2(new pcl::PointCloud<PointT>);
    pcl::io::loadPCDFile("read2.pcd", *cloud2);

    // 定义对象
    pcl::visualization::PCLVisualizer viewer; 
    //设置背景颜色，默认黑色
    viewer.setBackgroundColor(100, 100, 100); // rgb

    // --- 显示点云数据 ----
    // "cloud1" 为显示id，默认cloud,显示多个点云时用默认会报警告。
    viewer.addPointCloud(cloud1, "cloud1"); 

    pcl::visualization::PointCloudColorHandlerCustom<PointT> red(cloud2, 255, 0, 0); // rgb
    // 将点云设置颜色，默认白色
    viewer.addPointCloud(cloud2, red, "cloud2");

    // 将两个点连线
    PointT temp1 = cloud1->points[0];
    PointT temp2 = cloud1->points[1];
    viewer.addLine(temp1, temp2, "line0"); 
    // 同样可以设置线的颜色，
    //viewer.addLine(temp1, temp2, 255，0，0， "line0");

    // --- 显示网格数据 ---
    pcl::PolygonMesh mesh;
    pcl::io::loadPLYFile("read.ply", mesh);

    viewer.addPolygonMesh(mesh);


    // 开始显示2种方法,任选其一
    // 1. 阻塞式
    viewer.spin();

    // 2. 非阻塞式
    while (!viewer.wasStopped())
    {
        viewer.spinOnce(100);
        boost::this_thread::sleep(boost::posix_time::microseconds(100000));
        // 可添加其他操作
    }

    system("pause");
    return 0;
}

高级功能：设置回掉函数进行交互、显示区域分割

+ 按键事件

#include <pcl/io/pcd_io.h>
#include <pcl/visualization/pcl_visualizer.h>

// 回掉函数所用数据结构
struct callback_args {
    bool *isShow;
    pcl::PointCloud<pcl::PointXYZ>::Ptr orgin_points;
    pcl::visualization::PCLVisualizer::Ptr viewerPtr;
};

// 按键事件回掉函数
void kb_callback(const pcl::visualization::KeyboardEvent& event, void* args)
{
    if (event.keyDown() && event.getKeyCode() == 'a')
    {
        std::cout << "a has pressed" << std::endl;
        struct callback_args* data = (struct callback_args *)args;
        if (*(data->isShow))
        {
            data->viewerPtr->removePointCloud("cloud");
            *(data->isShow) = false;
            std::cout << "remove" << std::endl;
        }
        else {
            data->viewerPtr->addPointCloud(data->orgin_points, "cloud");
            *(data->isShow) = true;
            std::cout << "add" << std::endl;
        }
    }
}

int main(int argc, char** argv)
{
    pcl::PointCloud<pcl::PointXYZ>::Ptr cloud(new pcl::PointCloud<pcl::PointXYZ>);
    pcl::io::loadPCDFile("bunny.pcd", *cloud);
    pcl::console::print_highlight("load cloud !\n");

    // 定义对象
    pcl::visualization::PCLVisualizer::Ptr viewer(new pcl::visualization::PCLVisualizer);
    viewer->addPointCloud(cloud, "cloud");

    // 初始化参数
    bool isShow = true;
    struct callback_args kb_args;
    kb_args.isShow = &isShow;
    kb_args.orgin_points = cloud;
    kb_args.viewerPtr = viewer;

    // 设置回掉函数
    viewer->registerKeyboardCallback(kb_callback, (void*)&kb_args);

    viewer->spin();

    return 0;
}

+ 点选取事件

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

struct callback_args {
    // structure used to pass arguments to the callback function
    pcl::PointCloud<pcl::PointXYZ>::Ptr clicked_points_3d;
    pcl::visualization::PCLVisualizer::Ptr viewerPtr;
};

void pp_callback(const pcl::visualization::PointPickingEvent& event, void* args)
{
    struct callback_args* data = (struct callback_args *)args;

    if (event.getPointIndex() == -1)
        return;
    int index = event.getPointIndex();
    std::cout << "index: " << index << std::endl;
    pcl::PointXYZ current_point;
    event.getPoint(current_point.x, current_point.y, current_point.z);
    data->clicked_points_3d->points.push_back(current_point);
    // Draw clicked points in red:
    pcl::visualization::PointCloudColorHandlerCustom<pcl::PointXYZ> red(data->clicked_points_3d, 255, 0, 0);
    data->viewerPtr->removePointCloud("clicked_points");
    data->viewerPtr->addPointCloud(data->clicked_points_3d, red, "clicked_points");
    data->viewerPtr->setPointCloudRenderingProperties(pcl::visualization::PCL_VISUALIZER_POINT_SIZE, 10, "clicked_points");
    std::cout << current_point.x << " " << current_point.y << " " << current_point.z << std::endl;
}

int main(int argc, char** argv)
{
    pcl::PointCloud<pcl::PointXYZ>::Ptr cloud(new pcl::PointCloud<pcl::PointXYZ>);
    pcl::io::loadPCDFile("bunny.pcd", *cloud);
    pcl::console::print_highlight("load cloud !\n");

    pcl::visualization::PCLVisualizer viewer;

    pcl::visualization::PointCloudColorHandlerCustom<pcl::PointXYZ> green(cloud, 0, 255, 0);
    viewer.addPointCloud(cloud, green, "cloud");

    // Add point picking callback to viewer:
    struct callback_args cb_args;
    pcl::PointCloud<pcl::PointXYZ>::Ptr clicked_points_3d(new pcl::PointCloud<pcl::PointXYZ>);
    cb_args.clicked_points_3d = clicked_points_3d;
    cb_args.viewerPtr = pcl::visualization::PCLVisualizer::Ptr(&viewer);
    viewer.registerPointPickingCallback(pp_callback, (void*)&cb_args);
    pcl::console::print_highlight("Shift+click on three floor points, then press 'Q'...\n");

    // Spin until 'Q' is pressed:
    viewer.spin();

    system("pause");
    return 0;
}

+ 区域选取事件

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

struct callback_args{
    // structure used to pass arguments to the callback function
    pcl::PointCloud<pcl::PointXYZ>::Ptr orgin_points;
    pcl::PointCloud<pcl::PointXYZ>::Ptr chosed_points_3d;
    pcl::visualization::PCLVisualizer::Ptr viewerPtr;
};

void ap_callback(const pcl::visualization::AreaPickingEvent& event, void* args)
{
    struct callback_args* data = (struct callback_args *)args;
    std::vector<int> indiecs;

    if (!event.getPointsIndices(indiecs))
        return;
    for (int i = 0; i < indiecs.size(); ++i)
    {
        data->chosed_points_3d->push_back(data->orgin_points->points[indiecs[i]]);
    }

    // Draw clicked points in red:
    pcl::visualization::PointCloudColorHandlerCustom<pcl::PointXYZ> red(data->chosed_points_3d, 255, 0, 0);
    data->viewerPtr->removePointCloud("chosed_points");
    data->viewerPtr->addPointCloud(data->chosed_points_3d, red, "chosed_points");
    data->viewerPtr->setPointCloudRenderingProperties(pcl::visualization::PCL_VISUALIZER_POINT_SIZE, 5, "chosed_points");
    std::cout << "selected " << indiecs.size() << " points , now sum is " << data->chosed_points_3d->size() << std::endl;
}

int main(int argc, char** argv)
{
    pcl::PointCloud<pcl::PointXYZ>::Ptr cloud(new pcl::PointCloud<pcl::PointXYZ>);
    pcl::io::loadPCDFile("rabbit.pcd", *cloud);
    pcl::console::print_highlight("load cloud !\n");

    pcl::visualization::PCLVisualizer viewer;

    pcl::visualization::PointCloudColorHandlerCustom<pcl::PointXYZ> green(cloud, 0, 255, 0);
    viewer.addPointCloud(cloud, green, "cloud");

    // Add point picking callback to viewer:
    struct callback_args cb_args;
    cb_args.orgin_points = cloud;
    pcl::PointCloud<pcl::PointXYZ>::Ptr chosed_points_3d(new pcl::PointCloud<pcl::PointXYZ>);
    cb_args.chosed_points_3d = chosed_points_3d;
    cb_args.viewerPtr = pcl::visualization::PCLVisualizer::Ptr(&viewer);
    viewer.registerAreaPickingCallback(ap_callback, (void*)&cb_args);
    pcl::console::print_highlight("press x enter slected model, then press 'qQ'...\n");

    // Spin until 'Q' is pressed:
    viewer.spin();

    system("pause");
    return 0;
}

+ 显示区域分割

pcl可以将显示区域分割，从(xmin,ymin)到(xmax,ymax)一个矩形区域，范围是（0，1）。左下角(0,0)，右上角(1,1)。之前所有的函数都支持区域显示。

#include <pcl/io/pcd_io.h>
#include <pcl/point_types.h>
// 包含相关头文件
#include <pcl/visualization/pcl_visualizer.h>

typedef pcl::PointXYZ PointT;

int main()
{
    // 读取点云
    pcl::PointCloud<PointT>::Ptr cloud(new pcl::PointCloud<PointT>);
    pcl::io::loadPCDFile("read.pcd", *cloud);

    // 定义对象
    pcl::visualization::PCLVisualizer viewer; 

    int v1(1); // viewport
    viewer.createViewPort(0.0, 0.0, 0.5, 1.0, v1);
    viewer.setBackgroundColor(255, 0, 0, v1);
    viewer.addPointCloud(cloud, "cloud1", v1);;

    int v2(2);// viewport
    viewer.createViewPort(0.5, 0.0, 1.0, 1.0, v1);
    viewer.setBackgroundColor(0, 255, 0, v2);
    viewer.addPointCloud(cloud, "cloud2", v2);;

    viewer.spin();

    system("pause");
    return 0;
}

• pcl::visualization::CloudViewer

#include <pcl/io/pcd_io.h>
#include <pcl/point_types.h>
// 包含相关头文件
#include <pcl/visualization/cloud_viewer.h>

typedef pcl::PointXYZ PointT;

int main()
{
    // 读取点云
    pcl::PointCloud<PointT>::Ptr cloud(new pcl::PointCloud<PointT>);
    pcl::io::loadPCDFile("read.pcd", *cloud);

    pcl::visualization::CloudViewer viewer("simple cloud viewer");
    viewer.showCloud(cloud);
    while (!viewer.wasStopped())
    {
        // todo::
    }

    system("pause");
    return 0;
}