Options for realization A 3D Cadastre model could be formed by the LADM. However, LADM is still allowing many options and these should be investigated. Below a range of options for a 3D Cadastre model (and different countries could select different optimal solutions, depending on the actual situation and requirements): Minimalistic 3D Cadastre: do not consider cables, pipelines and (rail)roads as real estate objects (and do not register them in the cadastre), this eliminates the majority of subsurface objects. For apartment buildings: make them available via layers (by clicking on a symbol on 2D map/floor plans as in Spain) and on every floor there can be multiple units, that is vertical subdivision. This takes care of the majority of above surface objects. For all other 3D objects add a symbol to the 2D map and refer to the spatial source document (and other tricks to make the situation 'clear'). Advantage: easy to implement. Drawback: the minority of 3D exception cases (non layered apartments or pipelines and cables) may give the majority of problems. Topographic 3D Cadastre: do not create own geometry for the legal objects, but define the legal objects by referring to (boundaries) of physical objects (topography, including pipelines and cables). Advantage: when a reliable 3D topographic data set is available, this can also form the basis of the 3D Cadastre. Drawbacks: This implies that a legal object can only exist if there is a topographic counterpart to refer to. The topographic 3D Cadastre is non-consistent with the design principles of most of the existing 2D Cadastres. Polyhedral Legal 3D Cadastre: 3D volume parcels have their own geometry, similar as in the current 2D database (via polygons). However, this time the geometry is represented by a polyhedron (volume bound by flat faces). Advantages: relatively easy implementable with current technology (database, GIS/CAD), and similar to polygon approach in 2D. Drawbacks: no topology structure (for better quality guarantees) and no curved faces. Non-polyhedral Legal 3D Cadastre: similar to the previous model alternative, but now allowing curved faces, such as cylinder and spherical patches (which can be the result of buffers) of even more complicated curved surfaces, including NURBS. Advantage: more types of 3D shapes can be registered (as needed in Queensland, because the law and regulations do not enforce restrictions on the geometry types). Drawbacks: not so easily implemented with current technology and also still no topology structure. Topological Legal 3D Cadastre: 3D volume parcels are described by a topological structure based on node, edge, face and volume primitives. It is assumed that, and most useful when, the 3D objects constitute a partition of space. That is, the 3D objects have touching neighbours on all sides. Advantages: no redundancy in storing the boundaries, good quality control (no overlap and gaps). Drawbacks: less well supported by current technology. Note that two options are possible: with and without curved boundaries: edges and faces, e.g. NURBS. The different options all have their effect on data collection as they provide conditions what to collect. Similar to the 2D situation, it must be be decided how precise/accurate to collect 3D data. As it are legal spaces, can they already be identified in the planning phase or do they have to be collected (again) at the completion of construction? Again, note that there is a difference in the models of the legal object and the physical object, but the legal and physical reality should be related. Investigations will be conducted towards efficient procedures/workflow for 3D cadastral object registration and related business processes across the various countries. For example: What is the use of sketches/survey plans (of above and below surface 3D parcels)? What is the role of surveyors in 3D subdivisions or 3D parcel creation as this is currently not clear and has certainly not been standardized well in most countries.