Ask Your Question

Waiting for "gazebo_msgs/GetLinkState" causes Python to freeze

asked 2016-07-25 19:30:52 -0600

jwatson_utah_edu gravatar image

ROS Indigo on Ubuntu 14.04 with Gazebo 7.3.0 and Python 2.7:

I have an issue withs starting a Gazebo service proxy for getting link states programmatically from a Python file I run after running the launch file that starts the Gazebo world. At the top of the file I have:

from gazebo_msgs.srv import GetLinkState 
from gazebo_msgs.msg import LinkState # For getting information about link states


Later in the file I have:

# Get model information from Gazebo
# Get a handle to the Gazebo model spawner
model_info_prox = rospy.ServiceProxy('gazebo_msgs/GetLinkState', GetLinkState) # No error here
rospy.wait_for_service('gazebo_msgs/GetLinkState') # <-- Python hangs here without error
print model_info_prox( "lbr4_allegro" , "lbr4_7_link" ) # Never makes it here

The script freezes waiting for link states to become available, as noted above. Why does this happen? I used a similar pattern for spawning models and it works fine.

edit retag flag offensive close merge delete



Have you confirmed that the service exists? (Is it listed in 'rosservice list'?)

NEngelhard gravatar image NEngelhard  ( 2016-07-26 02:12:22 -0600 )edit

No, I had not. I grabbed the service name from a post elsewhere online. I was able to find the correct servive with rosservice list. See below. Thanks, @NEngelhard

jwatson_utah_edu gravatar image jwatson_utah_edu  ( 2016-07-26 17:24:10 -0600 )edit

1 Answer

Sort by ยป oldest newest most voted

answered 2016-07-26 17:35:56 -0600

jwatson_utah_edu gravatar image
  • The problem is that the name of the service is incorrect. In Gazebo 7.3, the /gazebo/get_link_state service is offered, according to rosservice list. As written above, the node will be waiting for a service that will never start.
  • The link name should be scoped with the model in a single name, not split into two names.
  • Also, the link state service requires a reference frame with respect to which the link pose will be reported.

The last three lines should be:

model_info_prox = rospy.ServiceProxy('/gazebo/get_link_state', GetLinkState)
print "Link 7 Pose:"    , endl , model_info_prox( "lbr4_allegro::lbr4_7_link" , "world" )
edit flag offensive delete link more

Your Answer

Please start posting anonymously - your entry will be published after you log in or create a new account.

Add Answer

Question Tools

1 follower


Asked: 2016-07-25 19:30:52 -0600

Seen: 837 times

Last updated: Jul 26 '16