What is the purpose of base_footprint?

Question

What purpose does the base_footprint link serve?

I'm reading through the Gazebo simulation tutorial, and it instructs the user to create an infinitesimally small nearly weightless box which is linked to the base_link, but it doesn't explain what this is or what it's used for, nor does it link to any resources that do. I did see this similar question, but that answer doesn't really explain why such a link is used. Why does any part of ROS need to know how the model projects onto the ground?

Does every Gazebo model require this link?

Edit: I've noticed the joint linking the footprint to the base_link has an origin whose z component represents a fixed distance from the ground. What value do you use for a legged model that doesn't have a fixed distance from the ground?

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Originally posted by Cerin on ROS Answers with karma: 940 on 2015-04-27

Post score: 4

Answer 1

In addition to some empirical answers, there's a REP-120 that defines base_footprint link.

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Originally posted by 130s with karma: 10937 on 2015-05-01

This answer was ACCEPTED on the original site

Post score: 6

Answer 2

I believe it is to be viewed as a stable projection onto the ground plane(z=0) used for object avoidance and such.Not sure if it needs to be limited to the base link in terms of size of the projection in this since it could treat like a bounding box that it is attached as a child link of the base link.

Ans: updated based on comments.

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Originally posted by rnunziata with karma: 713 on 2015-04-27

This answer was NOT ACCEPTED on the original site

Post score: 5

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Original comments

Comment by Cerin on 2015-04-29:
All the examples are for wheeled platforms and so used a fixed z for the base_footprint joint. What do you use for a legged model whose distance from the ground constantly varies?

Comment by dornhege on 2015-04-29:
base_footprint should always be at z 0. The thing that varies in that case is the transform base_footprint -> base_link.

Comment by Cerin on 2015-04-29:
In the tutorial link I posted, the example uses a non-zero value for z in the base_footprint_joint origin.

Comment by 130s on 2015-05-01:
Since base_footprint_joint seems to be a joint, not a link, it can have non-zero z value.

Answer 3

footprint allows your robot to avoid the obstacles , base_footprint should be used for transform the base_footprint coordinates to robot base and calculation the distance between your robot base and obstacle . for Simulation realty and auto calculating , that should use , I guess ..

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Originally posted by Atilay Mayadag with karma: 13 on 2015-04-27

This answer was NOT ACCEPTED on the original site

Post score: 1