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Rospy callback attribute error

asked 2017-11-24 05:48:02 -0600

OperationCrossbow gravatar image

Am following a youtube tutorial ( https://www.youtube.com/watch?v=DLVyc... ) with my own code:

Executable:

import rospy
from tf2_msgs.msg import TFMessage
import math #mathsssss
def callback(msg): #global cariable
    x = msg.transforms.transform.translation.x
    y = msg.transforms.transform.translation.y
    rospy.loginfo('x: {}, y: {}'.format(x,y))
def main():
    rospy.init_node('location_monitor')  #makes this code into a ROS node
    rospy.Subscriber("/tf", TFMessage, callback)
    # to sub: give (name of topic, messageclass, callback you want to do
    rospy.spin() # loop
if __name__ == '__main__':
    main()

Shell returns:

[ERROR] [1511523182.758203]: bad callback: <function callback at 0x7f1cd923e668>
Traceback (most recent call last):
  File "/opt/ros/kinetic/lib/python2.7/dist-packages/rospy/topics.py", line 750, in _invoke_callback
    cb(msg)
  File "/home/username/catkin_ws/src/pkgname/src/location_monitor_node.py", line 9, in callback
    x = msg.transforms.translation.x
AttributeError: 'list' object has no attribute 'translation'

Have searched other questions. Tried importing things from TFMessage, checking my capital letters, using it with .transform, and such. Nothing works. Am pretty new to ROS.

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2 Answers

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answered 2017-11-24 08:09:52 -0600

gvdhoorn gravatar image

According to the documentation for tf2_msgs/TFMessage (here), the transforms field is a list/array, so you'll need to index into it:

geometry_msgs/TransformStamped[] transforms

Something like msg.transforms[0].transform.translation.x.

But realise that you may receive multiple TransformStampeds in a single message, so always using the first might not be what you want.

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1

Note btw that subscribing to /tf like that is not typical usage. It's possible, but you might want to use the tf2 infrastructure (with Listeners, Buffers, etc).

gvdhoorn gravatar imagegvdhoorn ( 2017-11-24 08:11:11 -0600 )edit
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answered 2019-02-25 07:35:52 -0600

Richard Christo gravatar image

Hello, right now i am doing my project which is a 3 d printed arm robot and connected to my laptop using USB2dynamixel. I want to control this robot using MoveIt, but everytime I want to launch the robot_state.launch, this error always comes up

Traceback (most recent call last): File "/opt/ros/kinetic/lib/python2.7/dist-packages/rospy/topics.py", line 750, in _invoke_callback cb(msg) File "/home/richard/robot_ws/src/dxl_tutorial/scripts/state_publisher.py", line 37, in process joint_states.position.append((x.position-offset[x.id-1])(300.0/1023)(pi/180)) IndexError: list index out of range

I have already checked the state_publisher.py, but it seems like there is nothing wrong there. Can somebody please give some advice? I am also new to ROS.

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1

This does not seem related to the issue posted here in this Q&A.

Please don't post questions as answers, but post a new question.

gvdhoorn gravatar imagegvdhoorn ( 2019-02-25 08:25:07 -0600 )edit

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Asked: 2017-11-24 05:48:02 -0600

Seen: 1,094 times

Last updated: Feb 25