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。

类一：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("0010.pcd", *cloud1);pcl::PointCloud<PointT>::Ptr cloud2(new pcl::PointCloud<PointT>);pcl::io::loadPCDFile("0020.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。pcl::visualization::PointCloudColorHandlerCustom<PointT> green(cloud2, 0, 255, 0); // rgbviewer.addPointCloud(cloud1, green, "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[1000];//viewer.addLine(temp1, temp2, "line0"); // 同样可以设置线的颜色，蓝色viewer.addLine(temp1, temp2, 0, 0, 255, "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;
}

效果图

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;
}

这段代码实现了按下a清空显示，再按下重新显示。
主要设置回掉函数实现

viewer->registerKeyboardCallback(kb_callback, (void*)&kb_args);

kb_callback实现具体功能。

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 functionpcl::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;
}

效果图

按下shfit并点击某个点会将坐标打印出来。

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 functionpcl::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); // viewportviewer.createViewPort(0.0, 0.0, 0.5, 1.0, v1);viewer.setBackgroundColor(255, 0, 0, v1);viewer.addPointCloud(cloud, "cloud1", v1);;int v2(2);// viewportviewer.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;
}

类二：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;
}