Pose of the plane in device space.
The position of the plane generally stays the same between frames, unless the
understanding of where the plane is changes. For example, the device's plane
detection algorithm may determine that the surface associated with the plane
is actualy lower than it originally thought. In this case, the position's Y
value might change. But if the dimensions of the plane change as the surface
is explored, the position will likely stay the same. This is different than
the Center which can change frequently.
Thus, the Pose.position provides a stable reference point to which you could make other GameObjects relative.
A rotation of identity means the plane is horizontal, with its normal pointing up
(positive along the Y axis). The BoundedPlane.Width corresponds to its size in the X direction, and its BoundedPlane.Height corresponds to its size in the Z direction.