Height Systems for 3D Cadastres

3D systems are built assuming the existence of suitable height reference systems. However, the earth is neither homogeneous nor flat, the plumb lines are curved and not parallel and the definition of height and the implementation of geodetic height systems is complex. 3D cadastral systems have the same problem. Cadastral systems are designed to persist for centuries. Them the earth itself is changing and this needs to be considered in the system design. The paper starts with a discussion of existing height systems and the determination of height. Afterwards quality requirements for height in a 3D cadastral system are determined using some typical examples. The examples range from a tunnel below the Alps (e.g., the Gotthard base tunnel) to apartments in an apartment building. Deviations must be considered when creating the height system. The paper gives some indication where problems may occur and which pitfalls should be avoided