How to subscribe to a topic whom type is gazebo_msg/ContactState

asked 2016-09-24 07:22:23 -0600

Masoud
39 ●14 ●15 ●18

updated 2016-09-25 04:24:57 -0600

Hi everybody

I'm trying to write a subscriber following this tutorial) to listen to a topic which is published by a contact sensor (libgazebo_ros_bumper.so). Here is the structure of this topic shown in "topic monitor":

image description

Assuming that we want to write the size of ContactState message published by this topic, I wrote this program and compiled it (using catkin_make command) successfully:

#include "ros/ros.h"
#include "std_msgs/String.h"
#include "gazebo_msgs/ContactState.h"
#include <sstream>

void chatterCallback(const gazebo_msgs::ContactState cs)
{
  int a;
  a = sizeof(cs);
  std::stringstream ss;
  ss << a;
  ROS_INFO("The size of recieved ContactState message is: %d", a);
}

int main(int argc, char **argv)
{

  ros::init(argc, argv, "listener");
  ros::NodeHandle n;
  ros::Subscriber sub = n.subscribe("contact_sensor_state", 1000, chatterCallback);
  ros::spin();

  return 0;
}

However, Nothing happen whenever I run this subscriber node using rosrun command. It seems that ROS never call chatterCallback function. How should I edit ros::Subscriber sub = n.subscribe("contact_sensor_state", 1000, chatterCallback); to fix this issue?

I also have 2 more simple question regarding the above question:

1) How can I store the valued published by "contact_sensor_state/states/[0]/total_wrench/force/z" in a double variable in my program? (Shay answered this question)

2) Is it possible to advertise a variable in my program? I mean is it possible for a node to be both a subscriber and publisher. If yes, how should I edit the code to do this? (Shay answered this question)

I'm using ROS indigo, gazebo 2.2 and ubuntu 14.04.

Thanks

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answered 2016-09-24 08:00:31 -0600

Shay

763 ●4 ●11 ●19

updated 2016-09-24 08:14:31 -0600

The message variable should be a reference variable. You can refer to the code below.

#include "ros/ros.h"
#include "std_msgs/String.h"
#include "gazebo_msgs/ContactState.h"
#include <sstream>

void chatterCallback(const gazebo_msgs::ContactStateConstPtr& cs)
{
  int a;
  a = sizeof(cs);
  std::stringstream ss;
  ss << a;
  ROS_INFO("The size of recieved ContactState message is: %d", a);

  double z = cs->states[0].total_wrench.force.z; //here is for you question 1).
}

int main(int argc, char **argv)
{

  ros::init(argc, argv, "listener");
  ros::NodeHandle n;
  ros::Subscriber sub = n.subscribe("contact_sensor_state", 1000, chatterCallback);

  ros::Publisher pub = n.advertise<std_msgs::String>("mymsg",1000); //here is for you question 2).
  std_msgs::String msg = "Hello"; //here is for you question 2).

  ros::Rate loop_rate(10);

  while (ros::ok())
  {
      pub.publish(msg); //here is for you question 2).

      ros::spinOnce();
      loop_rate.sleep();
  }
  return 0;
}

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answered 2016-09-25 01:03:48 -0600

Masoud
39 ●14 ●15 ●18

Dear Shay and other ROS users,

Thanks for your attention. I replaced my code with the one that you provide and tried to compile it, but I got some error during compiling which made me to comment and edit some lines. Now, the final code that has been compiled successfully is as follow:

#include "ros/ros.h"
#include "std_msgs/String.h"
#include "gazebo_msgs/ContactState.h"
#include <sstream>

void chatterCallback(const gazebo_msgs::ContactState::ConstPtr& cs) // this line has been edited by adding "::" between ContactState and ConstPtr&
{
  int a;
  a = sizeof(cs);
  std::stringstream ss;
  ss << a;
  ROS_INFO("The size of recieved ContactState message is: %d", a);

  // double z = cs->states[0].total_wrench.force.z; // this line has been commented due to this error : ‘const struct gazebo_msgs::ContactState_<std::allocator<void> >’ has no member named ‘states’
}

int main(int argc, char **argv)
{

  ros::init(argc, argv, "listener");
  ros::NodeHandle n;
  ros::Subscriber sub = n.subscribe("contact_sensor_state", 1000, chatterCallback);

  ros::Publisher pub = n.advertise<std_msgs::String>("mymsg",1000); //here is for you question 2).
  std_msgs::String msg;
  msg.data = "Hello"; // this line has been edited due to this error: conversion from ‘const char [6]’ to non-scalar type ‘std_msgs::String’ requested

  ros::Rate loop_rate(10);

  while (ros::ok())
  {
      pub.publish(msg);

      ros::spinOnce();
      loop_rate.sleep();
  }
  return 0;
}

After executing this new code using rosrun, I realized that my main problem remains unsolved. I mean ROS don't call chatterCallback function as new messages published by "contact_sensor_state" :(

Does anybody knows what is the problem here? Isn't it better to specify type of topic in addition of it's name at ros::Subscriber sub = n.subscribe("contact_sensor_state", 1000, chatterCallback);. How should I edit this line to specify type of topic??

Hope for your help

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The subscribe() can only specify topic name, buffer length and callback function. I don't know why the chatterCallback didn't be called.

Shay ( 2016-09-25 02:16:34 -0600 )edit

Thank you shay... I tried subscribing to JointState (sensor_msg/JointState) topic by a similar code and it works well.. I don't know whats is the problem of ContactStates topic. Can I listen to the children's of ContactState topic (for example listening to "contact_sensor_state/states")?

Masoud ( 2016-09-25 02:50:10 -0600 )edit

Finally, I figured out what was the source of the problem. There was a mistype error in type of the message as well as the title of this question. I've dropped the letter "s" from "ContactsState" in my code...

I want to thank you Shay for your participation and good answers.

Masoud ( 2016-09-25 04:14:14 -0600 )edit

@_@..... yeah, I'm glad you solve it.

Shay ( 2016-09-25 06:04:16 -0600 )edit

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How to subscribe to a topic whom type is gazebo_msg/ContactState

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