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2014-07-10 19:22:29 -0500 asked a question tf/Tutorials/Introduction to tf: Error at launch

I am trying to run this tutorials but with no success. Here is the the info from the Terminal. Any suggestions (it is Hydro at 12.04, if that matters)?

Traceback (most recent call last): File "/opt/ros/hydro/lib/turtle_tf/", line 57, in <module> (trans, rot) = listener.lookupTransform('/turtle2', '/turtle1', rospy.Time()) tf.ExtrapolationException: Lookup would require extrapolation at time 1405037859.238833904, but only time 1405037859.238888979 is in the buffer, when looking up transform from frame [turtle1] to frame [turtle2] [turtle_pointer-6] process has died [pid 3634, exit code 1, cmd /opt/ros/hydro/lib/turtle_tf/ __name:=turtle_pointer __log:=/home/user/.ros/log/c3944f66-0890-11e4-928e-000c2947afe0/turtle_pointer-6.log]. log file: /home/user/.ros/log/c3944f66-0890-11e4-928e-000c2947afe0/turtle_pointer-6*.log Blockquote


Fixed this by introducing an artificial time delay here:

    turtle_vel = rospy.Publisher('turtle2/cmd_vel', geometry_msgs.msg.Twist)

Still, it probably should not be happening. What might be a better check?

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2014-06-19 01:49:17 -0500 asked a question How to Simultaneously Modify Parameters for Multiple Nodes?

Following this tutorial on "Understanding ROS Services and Parameters" (not allowed to add a link) (12.04, hydro)

Question: how can one use rosparam to affect more than one turtlesim? The lines below seem to affect only the one that was created last. What if I started three from different Terminals and wanted to change all the backgrounds in one action?

$ rosparam set background_r 150
$ rosservice call clear

Thank you