local position acceleration: use mean value between two publications

[NicolasM0]

Solved Problem

On our onboard computer, we use the vehicle local position message for estimation and control purpose.
We use the acceleration fields to have a higher order than just velocity and position.

We have observed aliasing on tests with vibrations. The NED acceleration integral become very different from the velocity.

Solution

To avoid aliasing on the NED acceleration, add an accumulation of acceleration to improve the down sampling.

This implementation looks like a hack... Of course, I'm open to any suggestions for a better implementation.

Test coverage

• Tested on an older branch (v1.14). It fixed our issue.
• Quickly tested on this commit in SITL, acceleration seems correct.

[bresch]

For navigation you could also rather use sensor_combined and for control you could get vehicle_acceleration

[bresch]

I think your changes makes sense as it's better to avoid aliasing anyways

[NicolasM0]

For navigation you could also rather use sensor_combined and for control you could get vehicle_acceleration

@bresch Thank you for the review.
I got the suggestion but to estimate a relative position in NED and generate a trajectory in ROS, I found easier to use only one topic with unbiased acceleration on my nodes than getting sensor_combined at full rate and doing the integration and rotation myself.