Definition of a ROI publisher with c++

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There is a pretty good tutorial describing how to write topic publishers in C++.

Here is a small code sample that should get you started. Note that you'll need to also set up a package, package.xml, and CMakeLists.txt as described here.

#include "ros/ros.h"
#include "sensor_msgs/RegionOfInterest.h"

int main(int argc, char **argv)
{
  ros::init(argc, argv, "faceROI");
  ros::NodeHandle n;

  ros::Publisher pub = n.advertise<sensor_msgs::RegionOfInterest>("faceROI", 1000);

  ros::Rate loop_rate(10);
  while (ros::ok())
  {
    <do your code to calculate Face ROI here>

    sensor_msgs::RegionOfInterest roi_msg;
    roi_msg.x_offset = 10;
    roi_msg.y_offset = 10;
    roi_msg.height = 200;
    roi_msg.width = 100;

    pub.publish(roi_msg);

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