Subscribing to global_costmap

edit

I have been trying out the navigation stack with the turtlebot tutorial. My objective is to be able to write a node (ex: costmap_subscriber_node.cpp) which subscribes to /move_base/global_costmap/costmap.

Example of node I am trying to write:

#include <ros/ros.h>

void occupancygrid_callback(const nav_msgs::OccupancyGrid::ConstPtr& msg){
      std::cout<< "occupancygrid_callback !! " << std::endl;
}

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

    ros::init(argc, argv, "costmap_subscriber");
    ros::NodeHandle nh;
    ros::Subscriber sub =
    nh.subscribe("/move_base/global_costmap/costmap_update",100,occupancygrid_callback);

    ros::Rate rate(60);
    while(nh.ok()){

          ros::spinOnce();
          rate.sleep();
    }

    return 0;
}

I checked first with the following command:

rostopic echo /move_base/global_costmap/costmap_updates

I get messages published every 5 seconds. The low frequency is the reason for the message:

rostopic hz /move_base/global_costmap/costmap
    subscribed to [/move_base/global_costmap/costmap]
    WARNING: may be using simulated time

However I am still unable to have my ros node callback pick up the messages. Similar problem here costmap-subscribe-problem-in-hydro.

Update

• I can subscribe to /map
• Output of roswtf gives :

ERROR The following nodes should be connected but aren't:
* /move_base->/move_base (/move_base/global_costmap/footprint)
* /move_base->/move_base (/move_base/local_costmap/footprint)