Ros同一局域网下多机通信

由于 ROS 底层是基于 TCP/IP 的，所以如果希望节点运行在不同的机器上，就需要设置好机器之间的网络连接。

1：

查看IP地址：ifconfig
查看主机名称：hostname

2：修改/etc/hosts文件：

目的是将 ip 与两台电脑的 hostname 绑定，两台电脑之间通过 hostname 就可以找到对方。修改之后，ping ip 和 ping hostname 都可

以找到对方的信息。

将本机 ip 和本机 hostname 以及另外机器的 ip 和 hostname 都添加进 /etc/hosts。注意，两个之间是 tab 键，不是空格。（所有机器都需要做）

注：ubuntu和zbxavier-desktop是hostname

3：重启网络： sudo /etc/init.d/networking restart

4：两台电脑上装上 chrony 包，实现同步 sudo apt-get install chrony

5：在计划作为 master 的电脑端输入$sudo gedit .bashrc 打开 bash 文件，添加

export ROS_HOSTNAME=ubuntu ＃ubuntu hostname
export ROS_MASTER_URI=http://ubuntu:11311

6：在从机的电脑端输入$sudo gedit .bashrc 打开 bash 文件，添加

export ROS_HOSTNAME=zbxavier ＃从机用户名
export ROS_MASTER_URI=http://ubuntu:11311 # 主机 URI

7：在主机端输入roscore 运行 ROS_MASTER，从机不能输入roscore 运行 ROS_MASTER。

（从机需要运行时roscore，注释掉export ROS_MASTER_URI=http://ubuntu:11311 即可【但是这样的话两台机器，分别输入rostopic list会发现两者的topic不一致，所以不建议】, 或者主机不要通过roscore启动ros，而是通过launch文件来启动，比如说通过启动realsense相机【这种方式两台机器输入rostopic list 发现topic list 完全一致，所以建议以这种方式】）

8：主/从机端发布/订阅话题

如：

rosrun ros_test_pkg image_publisher XXX

rosrun ros_test_pkg image_listener

9：传输图象时候是否压缩以及压缩算法的选择都可参考源码，写的很详细！

对应c++代码

# 图片发布代码 image_publisher.cpp#include <ros/ros.h>
#include <image_transport/image_transport.h>
#include <opencv2/highgui/highgui.hpp>
#include <cv_bridge/cv_bridge.h>
#include<ros/time.h>
//#include"opencv2/imgcodecs/legacy/constants_c.h"
int main(int argc, char** argv)
{ros::init(argc, argv, "image_publisher");ros::NodeHandle nh;image_transport::ImageTransport it(nh);auto pub = nh.advertise<sensor_msgs::CompressedImage>("a", 1);cv::Mat image = cv::imread(argv[1], CV_LOAD_IMAGE_COLOR);ROS_INFO("image size [%d, %d]", image.cols, image.rows);cv_bridge::CvImage cvimg(std_msgs::Header(), "bgr8", image);ros::Rate loop_rate(5);while (nh.ok()) {ros::Time begin = ros::Time::now();double secbegin=begin.toSec();ROS_INFO("I Published [%f]",secbegin);auto msg = cvimg.toCompressedImageMsg(cv_bridge::JPG);msg->header.stamp = begin;pub.publish(msg);ros::spinOnce();loop_rate.sleep();}
}

# 图片订阅代码 image_listener.cpp#include <ros/ros.h>
#include <image_transport/image_transport.h>
#include <opencv2/highgui/highgui.hpp>
#include <opencv2/opencv.hpp>
#include <cv_bridge/cv_bridge.h>
#include <ros/time.h>
//#include"opencv2/imgcodecs/legacy/constants_c.h"cv::Mat img_orig;void imageCallback(const sensor_msgs::CompressedImageConstPtr& msg)
{try{// 解压缩auto received_img = cv_bridge::toCvCopy(msg, "bgr8")->image;// 计时并显示ROS_INFO("recive cost :[%f sec]", ros::Time::now().toSec() - msg->header.stamp.toSec());ROS_INFO("image size %d, %d", received_img.cols, received_img.rows);ROS_INFO("img orig size %d %d", img_orig.cols, img_orig.rows);// 显示接收到的图像//cv::imshow("received_img", received_img);// 将原图与接收到的图像进行相减auto diff = cv::abs(img_orig - received_img);cv::Mat diff_norm;cv::normalize(diff, diff_norm, 0, 255, cv::NORM_MINMAX);cv::imwrite("diff_norm.bmp", diff_norm);cv::Mat diff_gray;cv::cvtColor(diff, diff_gray, cv::COLOR_BGR2GRAY);auto meanval = cv::mean(diff);double maxval;cv::Point maxloc;cv::minMaxLoc(diff_gray, 0, &maxval, 0, &maxloc);ROS_INFO("b mean %lf, g mean %lf, r mean %lf", meanval[0], meanval[1], meanval[2]);ROS_INFO("diff val %lf @ (%d, %d)", maxval, maxloc.x, maxloc.y);cv::imwrite("diff.bmp", diff);// 显示相减后的图像//cv::imshow("diff", diff);}catch (cv_bridge::Exception& e){}
}int main(int argc, char** argv)
{ros::init(argc, argv, "image_listener");ros::NodeHandle nh;//cv::namedWindow("received_img");//cv::namedWindow("diff");cv::startWindowThread();// 读取原图，必须与发送的图像一样，而且发送是BMP格式img_orig = cv::imread("1.bmp"); // 一定要发送bmp文件auto sub = nh.subscribe<sensor_msgs::CompressedImage>("a", 1, imageCallback);ros::spin();//cv::destroyWindow("received_img");//cv::destroyWindow("diff");
}

CMakeList.txt

cmake_minimum_required(VERSION 3.0.2)
project(ros_test_pkg)## Compile as C++11, supported in ROS Kinetic and newer
# add_compile_options(-std=c++11)## Find catkin macros and libraries
## if COMPONENTS list like find_package(catkin REQUIRED COMPONENTS xyz)
## is used, also find other catkin packages
find_package(catkin REQUIRED COMPONENTScv_bridgeimage_transportroscpprospystd_msgssensor_msgs
)
find_package(OpenCV REQUIRED)###################################
## catkin specific configuration ##
###################################
## The catkin_package macro generates cmake config files for your package
## Declare things to be passed to dependent projects
## INCLUDE_DIRS: uncomment this if your package contains header files
## LIBRARIES: libraries you create in this project that dependent projects also need
## CATKIN_DEPENDS: catkin_packages dependent projects also need
## DEPENDS: system dependencies of this project that dependent projects also need
catkin_package(
#  INCLUDE_DIRS include
#  LIBRARIES ros_test_pkg
#  CATKIN_DEPENDS roscpp std_msgs
#  DEPENDS system_lib
)###########
## Build ##
############# Specify additional locations of header files
## Your package locations should be listed before other locations
include_directories(
# include${catkin_INCLUDE_DIRS}
)#添加 ${OpenCV_INCLUDE_DIRS}
include_directories(./include${OpenCV_INCLUDE_DIRS}${catkin_INCLUDE_DIRS}${OpenCV_LIBRARY_DIRS}
)add_executable(image_publisher   ~/catkin_ws2/src/ros_test_pkg/src/image_publisher.cpp)
target_link_libraries(image_publisher${OpenCV_LIBRARIES} ${catkin_LIBRARIES}
)
# add_dependencies(image_publisher ) add_executable(image_listener  ~/catkin_ws2/src/ros_test_pkg/src/image_listener.cpp)
target_link_libraries(image_listener  ${OpenCV_LIBRARIES} ${catkin_LIBRARIES}
)
# add_dependencies(image_listener )

package.xml

<?xml version="1.0"?>
<package format="2"><name>ros_test_pkg</name><version>0.0.0</version><description>The ros_test_pkg package</description><!-- One maintainer tag required, multiple allowed, one person per tag --><!-- Example:  --><!-- <maintainer email="jane.doe@example.com">Jane Doe</maintainer> --><maintainer email="grzhang@todo.todo">grzhang</maintainer><!-- One license tag required, multiple allowed, one license per tag --><!-- Commonly used license strings: --><!--   BSD, MIT, Boost Software License, GPLv2, GPLv3, LGPLv2.1, LGPLv3 --><license>TODO</license><buildtool_depend>catkin</buildtool_depend><build_depend>cv_bridge</build_depend><build_depend>image_transport</build_depend><build_depend>roscpp</build_depend><build_depend>rospy</build_depend><build_depend>std_msgs</build_depend><build_depend>opencv2</build_depend><build_export_depend>cv_bridge</build_export_depend><build_export_depend>image_transport</build_export_depend><build_export_depend>roscpp</build_export_depend><build_export_depend>rospy</build_export_depend><build_export_depend>std_msgs</build_export_depend><build_export_depend>opencv2</build_export_depend> <exec_depend>cv_bridge</exec_depend><exec_depend>image_transport</exec_depend><exec_depend>roscpp</exec_depend><exec_depend>rospy</exec_depend><exec_depend>std_msgs</exec_depend><exec_depend>opencv2</exec_depend><!-- The export tag contains other, unspecified, tags --><export><!-- Other tools can request additional information be placed here --></export>
</package>