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Should tf frames exist at all times?

asked 2018-06-20 04:04:58 -0500

Mehdi. gravatar image

I am interested to know from the authors of TF if the nodes/joints in a tf tree are expected to exist during all the time the robot is up and running?

As an example: using tf to spawn new joints (for example object grasped will have its tf spawned, as a child node of the gripper) and then let it disappear once the grasped object is put down. Or imagine two robots that could dock to each other (like a locomotive and wagons) and then a link would be spawned between both robots.

would that infringe the rules of using tf? What would speak against it? And what would be an alternative solution in that case?

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answered 2018-06-20 12:47:28 -0500

tfoote gravatar image

updated 2018-06-20 12:47:41 -0500

It's completely find for frames to come and go from the system. It's designed to support that without incurring any overhead.

Attaching at a leaf is trivial, as you say you can just attach and detach something from the gripper by publishing the transform and then stopping.

If you want to join two different subtrees it's a little bit more complicated. Because you must join the root of one subtree to the other tree often you'll want to write a script that does this with the right semantic for your application. In your case of joining two subtrains.

There's a discussion of how to do that in #q293004

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Asked: 2018-06-20 04:04:58 -0500

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Last updated: Jun 20 '18