ROS2 lookupTransform() - cannot get transform at time now()

asked 2021-08-24 15:09:38 -0500

76 ●7 ●11 ●13

updated 2021-08-24 15:12:46 -0500

I am having issues acquiring transformation at the required time using lookupTransform()

It works as expected when I use tf2::TimePointZero (i.e. the last transform) but is failing when I use this->get_clock()->now() (i.e. transformation at "now").

Code snippet:

  transformStamped = tf_buffer_->lookupTransform(
    toFrameRel, fromFrameRel,
    this->get_clock()->now(),
    50ms);

The exception I handle is as follows:

Lookup would require extrapolation into the future. Requested time 1629833266.557150 but the latest data is at time 0.000000, when looking up transform from frame [turtle1] to frame [turtle2]

I actually spawn the turtle2 and definitely it needs some time to broadcast its transform, but the error is always there. Full code is available here: https://github.com/kurshakuz/geometry...

It also seems strange to me that the the latest data is at time 0.000000 is never changing.

Please let me know if you have any ideas.

answered 2021-08-24 15:13:37 -0500

tfoote

58457 ●128 ●550 ●526 http://www.ros.org/

Your problem isn't in the subscriber but the broadcaster where you're publishing the transforms with time zero.

https://github.com/kurshakuz/geometry...

You create the time object called "now" but you don't set the value to now, you just leave it default initialized which is time zero.

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Thanks a lot! That makes it clear. Should I simply assign the now variable to this->get_clock()->now()?

kurshakuz ( 2021-08-24 16:02:28 -0500 )edit

I expect that's what you want to do if you want that variable to represent the current time when publishing.

tfoote ( 2021-08-24 16:08:57 -0500 )edit

Can I ask you a similar question, but based on Python? What I am trying to do is to acquire transform at time now and change the variable at https://github.com/kurshakuz/geometry... to now = self.get_clock().now(). But I always get the Could not transform turtle1 to turtle2: Lookup would require extrapolation into the future. error even when I pass the timeout parameter using different values (from 0.05 to 5.0 seconds). Do you have any clue why is that may happen? The call is as below: now = self.get_clock().now() trans = self.tf_buffer.lookup_transform( to_frame_rel, from_frame_rel, now, timeout=Duration(seconds=1.0))

kurshakuz ( 2021-08-27 11:17:11 -0500 )edit

Please ask a new question with enough information to reproduce your problem. If you can make a reduced test case that can show the problem it's easiest to help you. Also look for other similar questions on this forum first. This type of question has been asked many times.

tfoote ( 2021-08-27 15:25:49 -0500 )edit

Do you mind to take a look at https://answers.ros.org/question/3853... ? I added additional explanations there.

kurshakuz ( 2021-08-30 12:55:53 -0500 )edit

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