Rviz | tf | scan - (No transform to fixed base)

Question

Hello all, I'm facing issues with scan data visualization on rviz. The following pictures show the problem:

image 1

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image 2

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As we can see from image 1, the transformation between the laser and base_link frames is defined, nevertheless rviz does not find this transformation and so can not display the scan data. To be more precisely, the reported message is:

Transform [sender=unknown_publisher]

and in sequece

For frame [laser]: No transform to fixed frame [base_link]. Tf error: [Lookup would require extrapolation to the future. Requested time 1469464365.119867794 but the latest data is at time 1469463838.127784645, when looking up transform from frame [laser] to frame [base_link]]

Well, I know that a lot of problems of visualizing data in rviz is related with timestemp and I a read a bunch of topic theads here, in the forum, but I do not realize how to solve this issue.

Here goes additional information and pictures:

The command:

rosrun tf tf_echo laser base_link

and

rosrun tf tf_echo base_link laser

runs without problem. But the command:

rosrun tf tf_monitor laser base_link

return a strange message that is:

RESULTS: for laser to base_link Chain is: odom -> base_link -> base_link -> base_link -> base_link -> base_link -> base_link -> base_link -> base_link ->

base_link Net delay avg = 0.350788: max = 0.548574

Frames: Frame: base_link published by unknown_publisher Average Delay: 0.400253 Max Delay: 0.400309 Frame: base_link published by unknown_publisher Average Delay: 0.400253 Max Delay: 0.400309 Frame: base_link published by unknown_publisher Average Delay: 0.400253 Max Delay: 0.400309 Frame: base_link published by unknown_publisher Average Delay: 0.400253 Max Delay: 0.400309 Frame: base_link published by unknown_publisher Average Delay: 0.400253 Max Delay: 0.400309 Frame: base_link published by unknown_publisher Average Delay: 0.400253 Max Delay: 0.400309 Frame: base_link published by unknown_publisher Average Delay: 0.400253 Max Delay: 0.400309 Frame: base_link published by unknown_publisher Average Delay: 0.400253 Max Delay: 0.400309 Frame: base_link published by unknown_publisher Average Delay: 0.400253 Max Delay: 0.400309

All Broadcasters: Node: unknown_publisher 256.402 Hz, Average Delay: 0.400246 Max Delay: 0.40031

as we can see, there is a strange loop behavior in the Chain (first line)

The using multiple machines, so maybe there is a problem with synchronization.

Any clue to where should I start or to what should I do to resolve this???

Thanks in advance!!!

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Originally posted by Randerson on ROS Answers with karma: 236 on 2016-07-25

Post score: 0

Answer 1

I found de origem of the problem. It was caused, as I suspect, by the time difference between the machines that were running the roscore and the tf transformation. I only synchronized them and I got the publication of the scan data stream on rviz.

Although I do no used, I think that I good solution is presented here.

For me, just as a first workaround, I used the command:

sudo ntpdate MACHINE_IP

where the MACHINE_IP variable contains the IP of the machine that used as reference to synchronize the other machines. (The command is executed in the machine that needs to be synchronized)

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Originally posted by Randerson with karma: 236 on 2016-08-01

This answer was ACCEPTED on the original site

Post score: 1