concatenate denotes series connection, in this tutorial, we will show concatenate two points and concatenate two fields.

• concatenate two fields:
  This means that two point clouds should have the same number of points.

• concatenate two points:
  This means taht two point clouds should have the same number of fields and the same data type of every field.

main.cpp

#include<iostream>
#include<pcl/io/pcd_io.h>
#include<pcl/point_types.h>

int main(int argc, char** argv)
{
    if(argc!=2)
    {
        std::cerr<<"Please specify command line argument '-f' or '-p'"<<std::endl;
        exit(0);
    }

    pcl::PointCloud<pcl::PointXYZ> cloud_a, cloud_b, cloud_c;
    pcl::PointCloud<pcl::Normal> n_cloud_b;
    pcl::PointCloud<pcl::PointNormal> p_n_cloud_c;

    cloud_a.width=5;
    cloud_a.height=cloud_b.height=n_cloud_b.height=1;
    cloud_a.points.resize(cloud_a.width*cloud_a.height);

    if(strcmp(argv[1],"-p")==0)
    {
        cloud_b.width=3;
        cloud_b.points.resize(cloud_b.width*cloud_b.height);
    }

    else if(strcmp(argv[1], "-f")==0)
    {
        n_cloud_b.width=5;
        n_cloud_b.points.resize(n_cloud_b.width*n_cloud_b.height);
    }

    else
    {
        std::cerr<<"Unknown argument!Please specify '-p' or '-f'"<<std::endl;
        exit(0);
    }

    for(size_t i=0; i<cloud_a.points.size(); ++i)
    {
        cloud_a.points[i].x=1024*rand()/(RAND_MAX + 1.0f);
        cloud_a.points[i].y=1024*rand()/(RAND_MAX + 1.0f);
        cloud_a.points[i].z=1024*rand()/(RAND_MAX + 1.0f);
    }

    if(strcmp(argv[1], "-p")==0)
    {
        for(size_t i=0; i<cloud_b.points.size(); ++i)
        {
            cloud_b.points[i].x=1024*rand()/(RAND_MAX + 1.0f);
            cloud_b.points[i].y=1024*rand()/(RAND_MAX + 1.0f);
            cloud_b.points[i].z=1024*rand()/(RAND_MAX + 1.0f);
        }
    }

    else if(strcmp(argv[1], "-f")==0)
    {
        for(size_t i=0; i<n_cloud_b.points.size(); ++i)
        {
            n_cloud_b.points[i].normal[0]=1024*rand()/(RAND_MAX + 1.0f);
            n_cloud_b.points[i].normal[1]=1024*rand()/(RAND_MAX + 1.0f);
            n_cloud_b.points[i].normal[2]=1024*rand()/(RAND_MAX + 1.0f);
        }
    }

    std::cerr<<"Cloud A: "<<std::endl;
    for(size_t i=0; i<cloud_a.points.size(); ++i)
    {
       std::cerr<<"     "<<cloud_a.points[i].x<<" "<<cloud_a.points[i].y<<" "
               <<cloud_a.points[i].z<<std::endl;
    }

    std::cerr<<"Cloud B: "<<std::endl;
    if(strcmp(argv[1], "-p")==0)
    {
        for(size_t i=0; i<cloud_b.points.size(); ++i)
        {
            std::cerr<<"    "<<cloud_b.points[i].x<<" "<<cloud_b.points[i].y<<" "
                    <<cloud_b.points[i].z<<std::endl;
        }
    }
    else if(strcmp(argv[1], "-f")==0)
    {
        for(size_t i=0; i<n_cloud_b.points.size(); ++i)
        {
            std::cerr<<"    "
                    <<n_cloud_b.points[i].normal[0]<<" "
                   <<n_cloud_b.points[i].normal[1]<<" "
                  <<n_cloud_b.points[i].normal[2]<<std::endl;
        }
    }


    std::cerr<<"Cloud C: "<<std::endl;
    // concatenate two points
    if(strcmp(argv[1], "-p")==0)
    {
        cloud_c  =cloud_a;
        cloud_c +=cloud_b;
        for(size_t i=0; i<cloud_c.points.size(); ++i)
        {
            std::cerr<<"    "
                    <<cloud_c.points[i].x<<" "
                   <<cloud_c.points[i].y<<" "
                  <<cloud_c.points[i].z<<std::endl;
        }
    }

    //concatenate two fields
    else if(strcmp(argv[1], "-f")==0)
    {
        pcl::concatenateFields(cloud_a, n_cloud_b, p_n_cloud_c);
        for(size_t i=0; i<p_n_cloud_c.points.size(); ++i)
        {
            std::cerr<<"    "
                    <<p_n_cloud_c.points[i].x<<" "
                   <<p_n_cloud_c.points[i].y<<" "
                  <<p_n_cloud_c.points[i].z<<" "
                 <<p_n_cloud_c.points[i].normal[0]<<" "
                <<p_n_cloud_c.points[i].normal[1]<<" "
               <<p_n_cloud_c.points[i].normal[2]<<std::endl;

        }
    }
    return 0;
}

CMakeLists.txt

cmake_minimum_required(VERSION 2.8)

project(concatenate_points)
find_package(PCL 1.2 REQUIRED)

include_directories(${PCL_INCLUDE_DIRS})
link_directories(${PCL_LIBRARY_DIRS})
add_definitions(${PCL_DEFINITIONS})

add_executable(${PROJECT_NAME} "main.cpp")
target_link_libraries(${PROJECT_NAME} ${PCL_LIBRARIES})

The execute results are as follows:

Screenshot from 2018-01-02 20-07-52.png

Screenshot from 2018-01-02 20-08-12.png