Ability to attach collision objects to collision objects?

[rr-tom-noble]

Is your feature request related to a problem? Please describe.

In our software, we have a need to attach tools to a robot.

Each tool is composed of separate parts, e.g. tool, connector, toolbit, some of which can be switched out with one another, requiring us to represent them as separate collision objects to avoid a combinatorial explosion of collision objects as more parts are added to the chain.

I think this is also nicer for modularity.

Describe the solution you'd like

It'd be nice to allow collision objects to be attached to other collision objects.

I'm unsure if this is already a feature in moveit. If so, we may be duplicating code (see alternatives).

It seems like this would be nearly identical to attaching the object to a link (i.e. specifying the name of the parent object and the transform relative to the parent object). When a query is made for the frame of the object relative to a frame which includes its parent object(s) as part of the transformation chain, the parent object transforms are also taken into account.

It'd probably also make sense for some operations to propagate to child objects, e.g.

• When an object is removed from the scene, all child objects are removed from the scene
• When an object is detached, all child objects are detatched

Describe alternatives you've considered

Our current solution involves keeping track of which collision objects are defined relative to other collision objects, and their relative transformations.

We attach all collision objects to the end-effector link of the robot, using the relative object to object transforms to compute the attach pose of children objects with respect to the end-effector link.

Additional context

No response