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How to get the data from Subscribers message with python

asked 2019-05-21 04:54:18 -0600

A_YIng gravatar image

Hello, In my program, I try to get the Pose msg data which publish from other topic.

But when I print the variable which to read the Subscribers message, I will get the all values are 0.

Here is my code:

import sys
import rospy 
import geometry_msgs.msg 
from geometry_msgs.msg import Pose 

grasp_goal = Pose()

def callback(msg):
    global grasp_goal
    grasp_goal = msg.grasp_goal

# Create a ROS node.
rospy.init_node('move_to_grasp', anonymous=True)
rospy.loginfo('Start to grasp the object...')

# Subscribe to the ROS topic that contains the grasp data.
sub = rospy.Subscriber('/grasp_pose', Pose, callback)

rospy.loginfo("x:%f y:%f z:%f w:%f x:%f y:%f z:%f", grasp_goal.position.x, grasp_goal.position.y, grasp_goal.position.z, grasp_goal.orientation.w, grasp_goal.orientation.x, grasp_goal.orientation.y, grasp_goal.orientation.z)

This is echo /grasp_pose topic: image description

This is result, all value are zero: image description

Thanks for your help !

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jayess gravatar image jayess  ( 2019-05-21 13:03:09 -0600 )edit

sorry for mistake, I will edit it.

A_YIng gravatar image A_YIng  ( 2019-05-21 22:06:19 -0600 )edit

1 Answer

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answered 2019-05-21 06:52:05 -0600

Your program is not waiting for a message to be received before it is printing out the pose information from the global variable. In order what your program is doing.

  1. intializes global variables 2, setup node 3, register subscriber (not the same as waiting for a message) 4, print values of global variables 5, shutdown

If you try printing out the values of the global pose variable in a 1 second loop, then you will see the correct values from messages being printed after the first message has been received. It might be a good idea to put a print in your callback, to confirm messages are being received too.

Hope this helps.

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Sorry, I'm still not sure what do you mean. Could you provide me some example code like this? It can help me know it clearly.

A_YIng gravatar image A_YIng  ( 2019-05-21 07:56:39 -0600 )edit

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Asked: 2019-05-21 04:54:18 -0600

Seen: 4,195 times

Last updated: May 21 '19