Hi @tungtwister, the position is given in mm whilst for the rotation, this represents an array of three floats, for the x, y and z rotation of the head of the user. The rotation is expressed in Euler angles using right-handed rotations around each axis. The z rotation describes the rotation around the vector pointing towards the user.
You can get further details with respec to the Core SDK streams @ https://github.com/Tobii/stream_engine/blob/master/docs/index.md
There is indeed a simple program you can run to demonstrate this graphically which I will send you via PM