Add indices to FollowJointTrajectory to store trajectory index being executed

[Levi-Armstrong]

This is to address issue #65

Open Question: Should it be storing an index for each joint or just a single index for all joints? I believe it is the former.

[destogl]

Open Question: Should it be storing an index for each joint or just a single index for all joints? I believe it is the former.

I think it is sufficient to have one index for all joints because the controllers usually take cases about individual points (all joints) they are passing through.

What is the exact purpose of these indices? Do we need a more descriptive field name?

[Levi-Armstrong]

Currently we use this for dynamic planning. So based on the environment if we are approaching a collision object we use this index to then look forward some time in the trajectory and replan a new segment and splice it in on the controller side. Another use case is if the tolerance violation is triggered during execution this index is useful for restarting the trajectory.

[bmagyar]

@Levi-Armstrong is this still required? Could you please document the new field please? The current name gives 0 clues to the user as to what they should be expecting those indices to correspond to and why.

[Levi-Armstrong]

@bmagyar

is this still required?

I would say yes. This is the index from the provided trajectory that the controller is executing toward. Though I don't think this needs to be a vector; do you agree?

Could you please document the new field please?

I will update the documentation.

[github-actions]

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[christophfroehlich]

@Levi-Armstrong is this still required? 🙈 I also think so, and we discussed this some time ago in a WG meeting. but I don't know if anyone reached out to you or anyone else at Southwest Research Institute

@bmagyar

is this still required?

I would say yes. This is the index from the provided trajectory that the controller is executing toward. Though I don't think this needs to be a vector; do you agree?

A scalar index should be enough right?

Could you please document the new field please?

I will update the documentation.

[Levi-Armstrong]

I believe it is still needed. I may have some time over the next month to make the requested changes.

[christophfroehlich]

The changes here in the control_msgs are quick, but we have to include that in the JTC then. Do you use ROS 2, or ROS 1 as the linked PR to ros_controllers?

[Levi-Armstrong]

Currently using both.

[saikishor]

@Levi-Armstrong why do you need a vector of indices? Isn't an index enough?

[Levi-Armstrong]

A don't think a vector is needed and only the index would be enough. I had asked a question related to this to see if anyone could think of any reason to keep the vector but not sure if I got any feedback.