ROS2 : 1/? Create a visual follower
===================================

We'll learn how launch ROS1 nodes with ROS2 nodes. In this example we'll see a follower robot with a camera (same concept as the sensorfollower but he will detect target with the color) in ROS2 with a node that allows object recognition.

Step 1 : Create the visual follower package
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We'll create a new package who allow the following of a visual target called ``pkg_visu`` and a new node ``visu.cpp``::

	ros2 pkg create --build-type ament_cmake pkg_visual --dependencies sensor_msgs geometry_msgs rclcpp OpenCV cv_bridge image_transport --node-name visual
	
.. note::
	parameters:
		- dependencies : parameter to declare dependencies
		- sensor_msgs : library to use sensor, in this tuto we'll use a camera
		- geometry_msgs : library to use variables like vector or poses
		- rclcpp : primary library, allow the use of ROS with c++
		- OpenCV : library allowing the exploitation of images
		- cv_bridge : library bridging opencv and ros
		- image_transport : Optimize and transport images
		- node : parameter to create nodes
		- visual : main node
		- DetectionCnam_codels : ??? (à modifier)
		
Step 2 : 
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Open on QtCreator and edit visu.cpp. You can delete all what is written. First, include the libraries::
	
	#include <cstdio>
	#include "opencv2/opencv.hpp"
	#include "rclcpp/rclcpp.hpp"
	#include "sensor_msgs/msg/image.hpp"
	#include "geometry_msgs/msg/twist.hpp"
	#include "cv_bridge/cv_bridge.h"
	
Now paste this universal main code::	
	
	int main(int argc, char ** argv)
	{
	  (void) argc;
	  (void) argv;
	  rclcpp::init(argc, argv);
	  rclcpp::spin(node);
	  rclcpp::shutdown();
	  return 0;
	}	
	
- init is the initialization
- spin is a loop of ``node`` which is not even declared
- shutdown is the end of execution

Now we'll create a class ``visual``, we'll declare inside this class	the main algorithm. Paste that between the ``include`` and the ``main()``::

	class Visu : public rclcpp::Node
	{

	};	
	
You can add the following line in the ``main`` before the ``spin``, it will define which node will be launched::

	auto node = std::make_shared<Visual>();