// %Tag(FULLTEXT)%
// %Tag(ROS_HEADER)%
#include "ros/ros.h"
// %EndTag(ROS_HEADER)%
// %Tag(MSG_HEADER)%
#include "std_msgs/String.h"
// %EndTag(MSG_HEADER)%
#include
/**
* This tutorial demonstrates simple sending of messages over the ROS system.
*/
int main(int argc, char **argv)
{
/**
* The ros::init() function needs to see argc and argv so that it can perform
* any ROS arguments and name remapping that were provided at the command line.
* For programmatic remappings you can use a different version of init() which takes
* remappings directly, but for most command-line programs, passing argc and argv is
* the easiest way to do it. The third argument to init() is the name of the node.
*
* You must call one of the versions of ros::init() before using any other
* part of the ROS system.
*/
// %Tag(INIT)%
ros::init(argc, argv, "talker");
// %EndTag(INIT)%
/**
* NodeHandle is the main access point to communications with the ROS system.
* The first NodeHandle constructed will fully initialize this node, and the last
* NodeHandle destructed will close down the node.
*/
// %Tag(NODEHANDLE)%
ros::NodeHandle n;
// %EndTag(NODEHANDLE)%
/**
* The advertise() function is how you tell ROS that you want to
* publish on a given topic name. This invokes a call to the ROS
* master node, which keeps a registry of who is publishing and who
* is subscribing. After this advertise() call is made, the master
* node will notify anyone who is trying to subscribe to this topic name,
* and they will in turn negotiate a peer-to-peer connection with this
* node. advertise() returns a Publisher object which allows you to
* publish messages on that topic through a call to publish(). Once
* all copies of the returned Publisher object are destroyed, the topic
* will be automatically unadvertised.
*
* The second parameter to advertise() is the size of the message queue
* used for publishing messages. If messages are published more quickly
* than we can send them, the number here specifies how many messages to
* buffer up before throwing some away.
*/
// %Tag(PUBLISHER)%
ros::Publisher chatter_pub = n.advertise<std_msgs::String>("chatter", 1000);
// %EndTag(PUBLISHER)%
// %Tag(LOOP_RATE)%
ros::Rate loop_rate(10);
// %EndTag(LOOP_RATE)%
/**
* A count of how many messages we have sent. This is used to create
* a unique string for each message.
*/
// %Tag(ROS_OK)%
int count = 0;
while (ros::ok())
{
// %EndTag(ROS_OK)%
/**
* This is a message object. You stuff it with data, and then publish it.
*/
// %Tag(FILL_MESSAGE)%
std_msgs::String msg;
std::stringstream ss;
ss << "hello world " << count;
msg.data = ss.str();
// %EndTag(FILL_MESSAGE)%
// %Tag(ROSCONSOLE)%
ROS_INFO("%s", msg.data.c_str());
// %EndTag(ROSCONSOLE)%
/**
* The publish() function is how you send messages. The parameter
* is the message object. The type of this object must agree with the type
* given as a template parameter to the advertise<>() call, as was done
* in the constructor above.
*/
// %Tag(PUBLISH)%
chatter_pub.publish(msg);
// %EndTag(PUBLISH)%
// %Tag(SPINONCE)%
ros::spinOnce();
// %EndTag(SPINONCE)%
// %Tag(RATE_SLEEP)%
loop_rate.sleep();
// %EndTag(RATE_SLEEP)%
++count;
}
return 0;
}
// %EndTag(FULLTEXT)%
ros::init(argc, argv, "talker");
初始化ROS,指定节点名称为“talker”,节点名称要保持唯一性。
ros::NodeHandle n;
实例化节点
问题:n与talker是什么关系?
理解:talker仅为节点名称,n为节点句柄用来处理后续给topic传递消息
ros::Publisher chatter_pub = n.advertise<std_msgs::String>("chatter", 1000);
定义了一个发布者,名字为chatter,数据类型为std_msgs::String,数值1000定义消息队列大小为1000,即超过1000条消息之后,旧的消息就会丢弃。
std_msgs::String msg;
定义了message object要与主题中的数据类型对应。
std::stringstream ss;
ss << "hello world " << count;
msg.data = ss.str();
定义了字符串流,可以把其他数据类型转换到string,例如本代码中的int count通过<<赋值与“hello world ”一同转化为string存入了ss中了
由于msg的变量为data,因而通过msg.data 利用ss.str()将ss中的值存入
ROS_INFO("%s", msg.data.c_str());
类似于C++中的std::cout用来输出打印信息,“%s”表明数据类型为String,由于msg.data的数据类型为string,因而可以通过c_str()来调用其中的值
chatter_pub.publish(msg);
发布消息,括号内为message object
ros::spinOnce();
回调一次,此处无任何卵用, 不是必需的,但是保持增加这个调用,是好习惯。
如果程序里也有订阅话题,就必需,否则回调函数不能起作用。
#include "ros/ros.h"
#include "std_msgs/String.h"
/**
* This tutorial demonstrates simple receipt of messages over the ROS system.
*/
void chatterCallback(const std_msgs::String::ConstPtr& msg)
{
ROS_INFO("I heard: [%s]", msg->data.c_str());
}
int main(int argc, char **argv)
{
/**
* The ros::init() function needs to see argc and argv so that it can perform
* any ROS arguments and name remapping that were provided at the command line.
* For programmatic remappings you can use a different version of init() which takes
* remappings directly, but for most command-line programs, passing argc and argv is
* the easiest way to do it. The third argument to init() is the name of the node.
*
* You must call one of the versions of ros::init() before using any other
* part of the ROS system.
*/
ros::init(argc, argv, "listener");
/**
* NodeHandle is the main access point to communications with the ROS system.
* The first NodeHandle constructed will fully initialize this node, and the last
* NodeHandle destructed will close down the node.
*/
ros::NodeHandle n;
/**
* The subscribe() call is how you tell ROS that you want to receive messages
* on a given topic. This invokes a call to the ROS
* master node, which keeps a registry of who is publishing and who
* is subscribing. Messages are passed to a callback function, here
* called chatterCallback. subscribe() returns a Subscriber object that you
* must hold on to until you want to unsubscribe. When all copies of the Subscriber
* object go out of scope, this callback will automatically be unsubscribed from
* this topic.
*
* The second parameter to the subscribe() function is the size of the message
* queue. If messages are arriving faster than they are being processed, this
* is the number of messages that will be buffered up before beginning to throw
* away the oldest ones.
*/
ros::Subscriber sub = n.subscribe("chatter", 1000, chatterCallback);
/**
* ros::spin() will enter a loop, pumping callbacks. With this version, all
* callbacks will be called from within this thread (the main one). ros::spin()
* will exit when Ctrl-C is pressed, or the node is shutdown by the master.
*/
ros::spin();
return 0;
}
订阅代码相对来说比较简单主要是写回调函数注意变量名称,主题名。
chatterCallback()
copy from https://www.jianshu.com/p/06e0e40cf6da.
特别感谢上面的作者,写了了1, 2, 3部分关于ROS下Pub与Sub的c++源文件编写,尤其是第三部分特别有用,直接促成了下面的MarkerPose c++源文件的编写成功。下文引用了上面链接中讲解的最重要的部分。
我们看回调函数。不熟悉C++的同学可能要会想为什么用这个函数的参数长这个样子。 (const std_msgs::String::ConstPtr& msg)什么鬼? 首先我得说,这个模式还是比较固定的,如果你要接受的是Int8类型的消息,那么参数会变成(const std_msgs::Int8::ConstPtr& msg)。ConstPtr代表一个指针。所以你目前要知道的是msg这个参数是你接收到的消息的指针就行了,同样这个名字你也随意改,但一般是…msg。所以你看到printf(ROS_INFO)中有msg->data这种调用方式。(在Publisher中我们定义了std_msgs::String对象msg,类包含数据成员data,调用方式为msg.data。如果类的指针叫msg,那么调用该成员的方式是msg->data)。所以现在msg->data就是一个std::string类型的量,假设有string类型的变量st要想print出来,代码就是printf("%s,", st.c_str() )(不能直接print st)。使用ROS_INFO其内部完全一样。
ljq@li2jq:~$ rostopic type /aruco_single/pose
geometry_msgs/PoseStamped
ljq@li2jq:~$ rosmsg show geometry_msgs/PoseStamped
std_msgs/Header header
uint32 seq
time stamp
string frame_id
geometry_msgs/Pose pose
geometry_msgs/Point position
float64 x
float64 y
float64 z
geometry_msgs/Quaternion orientation
float64 x
float64 y
float64 z
float64 w
对应topic的数据类型
ljq@li2jq:~$ rostopic type /chatter
std_msgs/String
ljq@li2jq:~$ rosmsg show st
std_msgs/ stereo_msgs/
ljq@li2jq:~$ rosmsg show st
std_msgs/ stereo_msgs/
ljq@li2jq:~$ rosmsg show std_msgs/String
string data
仿照参考
#include "ros/ros.h"
#include "std_msgs/String.h"
#include "geometry_msgs/PoseStamped.h"
/**
* This tutorial demonstrates simple receipt of messages over the ROS system.
*/
//参考sub文件写一个ArucoMarker Pose读取的subscribe
void MarkerCallback(const geometry_msgs::PoseStamped::ConstPtr& msg)
{
ROS_INFO("I heard the pose from the robot");
ROS_INFO("the position(x,y,z) is %f , %f, %f", msg->pose.position.x, msg->pose.position.y, msg->pose.position.z);
ROS_INFO("the orientation(x,y,z,w) is %f , %f, %f, %f", msg->pose.orientation.x, msg->pose.orientation.y, msg->pose.orientation.z, msg->pose.orientation.w);
ROS_INFO("the time we get the pose is %f", msg->header.stamp.sec + 1e-9*msg->header.stamp.nsec);
std::cout<<"\n \n"<<std::endl; //add two more blank row so that we can see the message more clearly
}
int main(int argc, char **argv)
{
/**
* The ros::init() function needs to see argc and argv so that it can perform
* any ROS arguments and name remapping that were provided at the command line.
* For programmatic remappings you can use a different version of init() which takes
* remappings directly, but for most command-line programs, passing argc and argv is
* the easiest way to do it. The third argument to init() is the name of the node.
*
* You must call one of the versions of ros::init() before using any other
* part of the ROS system.
*/
ros::init(argc, argv, "Marker");
/**
* NodeHandle is the main access point to communications with the ROS system.
* The first NodeHandle constructed will fully initialize this node, and the last
* NodeHandle destructed will close down the node.
*/
ros::NodeHandle n;
/**
* The subscribe() call is how you tell ROS that you want to receive messages
* on a given topic. This invokes a call to the ROS
* master node, which keeps a registry of who is publishing and who
* is subscribing. Messages are passed to a callback function, here
* called chatterCallback. subscribe() returns a Subscriber object that you
* must hold on to until you want to unsubscribe. When all copies of the Subscriber
* object go out of scope, this callback will automatically be unsubscribed from
* this topic.
*
* The second parameter to the subscribe() function is the size of the message
* queue. If messages are arriving faster than they are being processed, this
* is the number of messages that will be buffered up before beginning to throw
* away the oldest ones.
*/
ros::Subscriber Marke_sub = n.subscribe("aruco_single/pose", 1000, MarkerCallback);
/**
* ros::spin() will enter a loop, pumping callbacks. With this version, all
* callbacks will be called from within this thread (the main one). ros::spin()
* will exit when Ctrl-C is pressed, or the node is shutdown by the master.
*/
ros::spin();
return 0;
}
主体代码copy from listener.cpp文件,该代码实现了订阅Aruco_single/pose topic来查看Pose的信息,先通过两个launch命令启动kinect2摄像头与二维码识别:
roslaunch aruco_ros single.launch
roslaunch kinect2_bridge kinect2_bridge.launch
void MarkerCallback(const geometry_msgs::PoseStamped::ConstPtr& msg)
主要是参数部分的格式,const后面要与topic的type对应。
ros::Subscriber Marke_sub = n.subscribe("aruco_single/pose", 1000, MarkerCallback);
这个函数注意第一个参数为订阅的topic,前面没有(/)。