Added 1D kinematic state message.

[jrutgeer]

🎉 New feature

Required for gazebosim/gz-sim#2021

Summary

This PR adds a message type for 1D kinematic state:

• Position
• Velocity
• Acceleration
• Jerk

[mjcarroll]

@azeey and @scpeters any other input from a physics perspective?

[codecov]

Codecov Report

Merging #352 (0680992) into gz-msgs9 (2e7f1c6) will not change coverage.
The diff coverage is n/a.

❗ Current head 0680992 differs from pull request most recent head 073c121. Consider uploading reports for the commit 073c121 to get more accurate results

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[azeey]

Looking at gazebosim/gz-sim#2021, I only see position and velocity being populated. Have you considered using the existing Odometery message?

[jrutgeer]

@azeey Good question. The initial idea for gazebosim/gz-sim#2021 was that it would publish the full kinematic state, including acceleration and jerk. However, during implementation I realized that this is not possible as the TrackController is velocity resolved (i.e. at each timestep the position and velocity are known, but the acceleration depends on the next velocity setpoint, which is not yet known).

So technically it is possible to use the odometry message instead, at least for this usecase.

From a semantic point of view, I think initially it feels rather strange to use the odometry message, but having given it some thought I conclude that "conveyor position and velocity" is indeed a kind of "1D odometry", and similar arguments as in this discussion hold, so it might indeed make sense to represent a 1D odometry with the existing 6D odometry message.

If you follow this line of thought, I will close this PR and adapt gazebosim/gz-sim#2021 accordingly.

[jrutgeer]

Closing in favor of changing gazebosim/gz-sim#2021 to use an odometry message instead.