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Infrared

Description: Using infrared sensors on the evarobot.

Tutorial Level: BEGINNER

Next Tutorial: Sonar

Starting Infrared

Connect via SSH to the Evarobot.

> ssh pi@evarobotDSK
> sudo -s

Execute evarobot_infrared.launch file.

# evarobot
> roslaunch evarobot_infrared evarobot_infrared.launch

In order to sync ros masters,

# evarobot
> roslaunch master_discovery_fkie master_discovery.launch

# evarobot
> roslaunch master_sync_fkie master_sync.launch

Reading Infrared via Terminal

Execute synchronisation nodes, to reach evarobot ros master.

# pc
> roslaunch master_discovery_fkie master_discovery.launch

# pc
> roslaunch master_sync_fkie master_sync.launch

evarobot_infrared publishes /sensor/ir<n> topic where n is number of sensor. In this example, we will read sensor called 0.

# pc
> rostopic echo /sensor/ir0

To get information about the topic

# pc
> rostopic info /sensor/ir0

Writing a Simple Subscriber for Infrared

Use the catkin_create_pkg script to create a new package called 'evarobot_infrared_subs' which depends on sensor_msgs, roscpp, and rospy:

> cd ~/catkin_ws/src
> catkin_create_pkg evarobot_infrared_subs sensor_msgs rospy roscpp

Create a src directory in the evarobot_infrared_subs package directory.

> mkdir -p ~/catkin_ws/src/evarobot_infrared_subs/src

Create the src/infrared_listener.cpp file within the evarobot_infrared_subs package.

> cd ~/catkin_ws/src/evarobot_infrared_subs/src
> gedit infrared_listener.cpp

And paste the following inside infrared_listener.cpp:

   1 #include "ros/ros.h"
   2 #include "sensor_msgs/Range.h"
   3 
   4 /**
   5  * This tutorial demonstrates simple receipt of infrared sensor data over the ROS system.
   6  */
   7 
   8 /**
   9  * Callback function executes when new topic data comes.
  10  * Task of the callback function is to print data to screen.
  11  */
  12 void chatterCallback(const sensor_msgs::Range::ConstPtr& msg)
  13 {
  14   ROS_INFO("Infrared Seq: [%d]", msg->header.seq);
  15   ROS_INFO("Infrared Range: [%f]", msg->range);
  16 }
  17 
  18 int main(int argc, char **argv)
  19 {
  20   /**
  21    * The ros::init() function needs to see argc and argv so that it can perform
  22    * any ROS arguments and name remapping that were provided at the command line.
  23    * For programmatic remappings you can use a different version of init() which takes
  24    * remappings directly, but for most command-line programs, passing argc and argv is
  25    * the easiest way to do it.  The third argument to init() is the name of the node.
  26    *
  27    * You must call one of the versions of ros::init() before using any other
  28    * part of the ROS system.
  29    */
  30   ros::init(argc, argv, "infrared_listener");
  31 
  32   /**
  33    * NodeHandle is the main access point to communications with the ROS system.
  34    * The first NodeHandle constructed will fully initialize this node, and the last
  35    * NodeHandle destructed will close down the node.
  36    */
  37   ros::NodeHandle n;
  38 
  39   /**
  40    * The subscribe() call is how you tell ROS that you want to receive messages
  41    * on a given topic.  This invokes a call to the ROS
  42    * master node, which keeps a registry of who is publishing and who
  43    * is subscribing.  Messages are passed to a callback function, here
  44    * called chatterCallback.  subscribe() returns a Subscriber object that you
  45    * must hold on to until you want to unsubscribe.  When all copies of the Subscriber
  46    * object go out of scope, this callback will automatically be unsubscribed from
  47    * this topic.
  48    *
  49    * The second parameter to the subscribe() function is the size of the message
  50    * queue.  If messages are arriving faster than they are being processed, this
  51    * is the number of messages that will be buffered up before beginning to throw
  52    * away the oldest ones.
  53    */
  54   ros::Subscriber sub = n.subscribe("sensor/ir0", 1000, chatterCallback);
  55 
  56   /**
  57    * ros::spin() will enter a loop, pumping callbacks.  With this version, all
  58    * callbacks will be called from within this thread (the main one).  ros::spin()
  59    * will exit when Ctrl-C is pressed, or the node is shutdown by the master.
  60    */
  61   ros::spin();
  62 
  63   return 0;
  64 }

> cd ..
> gedit CMakeLists.txt

The generated CMakeLists.txt should look like this

cmake_minimum_required(VERSION 2.8.3)
project(evarobot_infrared_subs)

find_package(catkin REQUIRED COMPONENTS
  sensor_msgs
  roscpp
  rospy
)

catkin_package()

include_directories(
  ${catkin_INCLUDE_DIRS}
)

add_executable(infrared_listener src/infrared_listener.cpp)
add_dependencies(infrared_listener sensor_msgs_generate_messages_cpp)
 target_link_libraries(infrared_listener
   ${catkin_LIBRARIES}
 )

Now run catkin_make

> cd ~/catkin_ws/
> catkin_make

To run infrared_listener,

> rosrun evarobot_bumper_subs infrared_listener

Visualisation of Infrared Sensors

> rosrun rviz rviz


rviz_infrared.png



2019-04-20 12:24