Investigate z position of the map in 2D SLAM with IMU

[wohe]

Using 2D SLAM with an IMU, the tracking frame must be colocated with the IMU, i.e. its z position cannot be chosen arbitrarily.

It might be that the map is always shown with the z height of the tracking frame, i.e. the z height of the IMU. This might not be desirable, e.g. if the laser is mounted below the IMU.

It needs investigation whether the z position can or cannot be configured right now, or whether we have to add some way to make it configurable.

[BrannonKing]

Any progress on this?