Question Need simplest example of 2d sprite snapping to mesh

Can anyone point me to a simplest (ARkit) example of snapping a 2d sprite to mesh based on wherever the device camera is pointing?

ie reticle that rotates to the surface of whatever is hit by a Raycast.

I know it also involves TrackableTypes>
https://forum.unity.com/threads/difference-between-plane-trackabletypes.623956/

but can't get anything to work on both floor and ceiling meshed surfaces.
Any help appreciated!