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Version: QTrobot V1

QTrobot interfaces using ROS Subscribe

Overview

 Level:  Basic
 Goal:  learn how to read QTrobot interfaces in python via ROS Subscribers
 Requirements:

If you have followed our previous tutorials, you should know how to start coding on QTrobot with python and got the basic knowledge of ROS framework. In this tutorial we will learn about how to read some of QTrobot interfaces using ROS Subscribe.

Create a python project​

First we create a python project for our tutorial. let's call it tutorial_qt_subscribe and add the required python file:

cd ~/catkin_ws/src
catkin_create_pkg tutorial_qt_subscribe rospy roscpp -D "Read QTrobot data with ROS Subscribe"
cd tutorial_qt_subscribe/src
touch tutorial_qt_subscribe_node.py
chmod +x tutorial_qt_subscribe_node.py

QTrobot nuitrack interface - Gestures​

Open the tutorial_qt_subscribe_node.py file and the add the following code:

#!/usr/bin/env python3
import sys
import rospy
from qt_nuitrack_app.msg import Gestures

def gesture_callback(msg):
    rospy.loginfo(msg)

if __name__ == '__main__':
    rospy.init_node('my_tutorial_node')
    rospy.loginfo("my_tutorial_node started!")

    # define ros subscriber
    rospy.Subscriber('/qt_nuitrack_app/gestures', Gestures, gesture_callback)
   
    try:
        rospy.spin()
    except KeyboardInterrupt:
        pass

    rospy.loginfo("finsihed!")

First we imported Gestures message type from qt_nuitrack_app.msg message library. This message type is used in communication with /qt_nuitrack_app/gestures.

Tip

How do we know which messages an interface uses? well, There is a useful command in ROS which tells you that:

rostopic info /qt_nuitrack_app/gestures
Type: qt_nuitrack_app/Gestures
...

Then we created a subscriber for /qt_nuitrack_app/gestures with callback function gesture_callback to print any data that comes from that topic. Stand in front of QTrobot and do one of this gestures ("SWIPE UP", "SWIPE DOWN", "SWIPE LEFT", "SWIPE RIGHT"). When QTrobot detects you, the script should print something like this:

[INFO] [1629900965.371938]: gestures:
  -
    id: 2
    name: "SWIPE UP"