How to mark area?

[Puybaret]

You could use rooms where the floor and the ceiling is not visible (be cautious because the ceiling of a room can be viewed only from bottom in the 3D view).
You could also create a subclass of Room and change or override the method createObject3D in Object3DBranchFactory class to return an empty 3D object for this new class (just use an empty subclass of Object3DBranch).

[mrol]

Thank you, Emmanuel. I will try this.