A simple way of returning an UP vector

[RickPoleshuck]

Plugin

sensors_plus

Use case

I would like a simple way of returning a vector that shows which way is up that I can use to compare with acceleration vectors. Maybe the pub already provides a way to do this, but not an easy way. To be clear, UP is the direction opposite the dominant gravitational field.

Proposal

I am not at all sure how to do this.