PYTHON + ROS + V-REP

asked 2018-01-05 15:03:32 -0500

aefka
15 ●9 ●11 ●17

updated 2018-01-05 17:15:46 -0500

Hi I have got a problem with publish data. I want to publish msg.linear.x and msg.linear.y to V-REP via ROS.

When I write in terminal

rostopic pub -1 /cmd_vel geometry_msgs/Twist '{linear: {x: -3.0, y: -3.0}}'

Everything is ok, but I want to publish this from PYTHON.

My actually code is:

#!/usr/bin/env python
import rospy
from std_msgs.msg import String
#added
from geometry_msgs.msg import Twist 


def callback(data):
    global msg
    if data.data=="Unknown":
        pub = rospy.Publisher('cmd_vel', Twist) 
        rospy.loginfo("Classifiers output: %s in unknown" % data.data)
        msg.linear.x = 2
        msg.linear.y = 2
        msg.angular.z = 0
        speed = 0.4 
        rospy.loginfo("checking for cmd" + str(msg.linear))
        pub.publish(msg)
    elif data.data=="Check":
        rospy.loginfo("Classifiers output: %s in check" % data.data)
    else:      
        rospy.loginfo("Classifiers output: %s and not unknown or check" % data.data)



def listener():

     global msg
     rospy.init_node('listener', anonymous=True)
     msg = Twist()
     rospy.Subscriber("ccc", String, callback)
     rospy.spin()


if __name__ == '__main__':



    listener()

I am newbie in Python. Above code, I found on the Internet, and I try to translate into my case. What I want to do? I want to have control model in V-REP, by ROS. I can control by terminal thanks for egzample:

rostopic pub -1 /cmd_vel geometry_msgs/Twist '{linear: {x: -3.0, y: -3.0}}'

but I want control this model via Python, but I dont know how to do this :/

Thanks for suggestion

Comments

What is your question/problem? Is your code not working as expected?

jayess ( 2018-01-05 15:43:00 -0500 )edit

Yes :/ I want to publish msg.linear.x = 2 msg.linear.y = 2 from python. I am newbie in this language :/

aefka ( 2018-01-05 15:59:52 -0500 )edit

add a comment

answered 2018-01-05 15:51:07 -0500

jayess
6155 ●26 ●85 ●92

updated 2018-01-05 16:38:13 -0500

If you're having any issues with the publishing, part of the problem may be that you're creating your publisher inside of your callback function. What you should do is create it inside your listener function so you're not re-instantiating it every time your a message is published on the /ccc topic.

For example:

#!/usr/bin/env python
import rospy
from std_msgs.msg import String
#added
from geometry_msgs.msg import Twist 


def callback(data):
    global msg
    global pub
    if data.data=="Unknown":
        rospy.loginfo("Classifiers output: %s in unknown" % data.data)
        msg.linear.x = 2
        msg.linear.y = 2
        msg.angular.z = 0
        speed = 0.4 
        rospy.loginfo("checking for cmd" + str(msg.linear))
        pub.publish(msg)
    elif data.data=="Check":
        rospy.loginfo("Classifiers output: %s in check" % data.data)
    else:      
        rospy.loginfo("Classifiers output: %s and not unknown or check" % data.data)



def listener():
     global msg
     rospy.init_node('listener', anonymous=True)
     msg = Twist()
     rospy.Subscriber("ccc", String, callback)
     global pub
     pub = rospy.Publisher('cmd_vel', Twist, queue_size=10) # move instantiation of publisher
     rospy.spin()


if __name__ == '__main__':
    listener()

Although, what you most likely would want to do is create a class to do this since the use of globals isn't always the greatest of ideas.