Boundingbox on Link API

[jfelixre]

There is an alternative of Gazebo-classic's Link API Boundingbox function for ignition?

API reference page still shows a "TODO"

thanks!

[azeey]

We already have the ability to get the bounding box, but it's through a component. Documenting this would be a good step as well.

[gabrielfpacheco]

We already have the ability to get the bounding box, but it's through a component. Documenting this would be a good step as well.

@azeey, isn't that only available to get the model bounding box, since the Physics plugin set it here?

I couldn’t find any source that actually sets a gz::components::AxisAligned for a link entity. Therefore, as I had to get the bounding box of the link for a system plugin I developed, I created #2787 and gazebosim/sdformat#1547 to provide such an API.

Please let me know if I'm missing something, I hope this could be helpful to others.

[iche033]

I think the alternative approach would be to update the the physics system populate the bounding box component for links as well? I see the API available in gz-physics, GetLinkBoundingBox

[gabrielfpacheco]

I think the alternative approach would be to update the the physics system populate the bounding box component for links as well

Yes, I think this would probably be more straightforward. If I understood it correctly, this feature should be available for all currently supported physics engines, right?

I initially thought not to update the physics plugin because I did not want to add extra load to a critical plugin if this was not an actual requirement. However, I believe we could do the same as for the model and only update the link entities containing the corresponding components.

Maybe I could update #2787 to add this feature to the physics system and update the link API so that it only computes from the SDF if an AxisAlignedBox component does not exist for the link entity. Or I could completely remove the calculation via SDF if you think it is more adequate.

Please, let me know what would be the best path forward.

[iche033]

I think getting the bounding box info from the physics system is preferred because it has the information already, and there is no need for a custom mesh bounding box calculator. In the rare case the the users does not load a physics system in Gazebo (or a particular physics engine does not support the bounding box feature), we could then fall back to using the SDF API.

I think the first step is to implement a similar logic for populating a model AxisAlignedBox for links in the physics system. The expected usage here is that plugin writers would need to manually create the AxisAlignedBox component for a Link, the physics system then populates it.

We can then update the Link class to add the AxisAlignedBox API like you did in #2787, except we would be the one creating the AxisAlignedBox component for the link in that class. I think this could be done through an EnableBoundingBoxChecks call (similar to EnableVelocityChecks).

If you're ok with this approach, could you do the changes in the physics system in a separate PR? Mainly just to make the review process easier. Thanks for the contributions so far!

[gabrielfpacheco]

If you're ok with this approach, could you do the changes in the physics system in a separate PR? Mainly just to make the review process easier

Yeah, I like the suggested approach. As soon as I have some free cycles, I will make the changes to the open PR and open a new one for the physics.

Thanks for the contributions so far!

My pleasure :)