ISPRS, Vol.34, Part 2W2, “Dynamic and Multi-Dimensional GIS", Bangkok, May 23-25, 2001 
in Section 4, which also includes a discussion of some possible 
3D model extensions. Section 5 describes some of the issues 
involved in the 3D data collection and preparation, either based 
on CAD models created by designers or on surveying. Complex 
in this is the insertion of the 3D data into the current (2D) geo- 
DBMS. That is where are the 3D data located in respect to the 
2D data Some examples of integrated querying and viewing of 
2D and 3D data are given in Section 6. Finally, conclusions and 
future work are described in Section 7. 
2. THE CASE 
In the major urban centers (and especially their business 
districts) land use is becoming so intense, that very different 
types of ‘land’ use are being positioned under and above each 
other. Examples are: 
constructions on top of each other (see Figure 1); 
infrastructure above and under the ground; 
the increasing number of cables and pipes; 
the increasing number of owners of cables and pipes due 
to privatisation processes. 
Figure 1: various land use on top of each other 
With this tendency to use land more efficiently, the Kadaster, 
responsible for maintaining juridical boundaries and the legal 
status of real estates, is confronted with spatially complex 
property rights. Until now, the right of property of real estate is 
linked to the division of land in 2D parcels. A juridical horizontal 
division in land use can only be established by the registration of 
limited rights on the 2D surface parcel. Consequently, the use of 
land above and under the surface needs to be projected on the 
surface (see Figure 2). In some cases, it is even necessary to 
create new parcels on the surface to be able to define the legal 
status in 3D satisfactorily. 
are needed to register the legal status of one building 
Some of the complexities met with the registration of 3D 
situations in a land information system that was originally 
developed to register parcels, are the following (Stoter, 2000): 
registration is only an administrative one; 
the lack of a (digital) 3D representation of the situation 
makes it difficult to get insight in the factual situation; 
current registration is used in situations for which it was not 
originally meant; 
the current solutions lead to divers registration practices for 
similar situations; 
the parcel is used for registration and not the object on, 
above or under the surface (building, tunnel etc.). This 
means that these real-world objects are not registered as 
such. This leads to the following complications: 
the real-world object itself or characteristics of the 
object are not maintained and can therefore not be 
found at the cadastral registration system: the real 
world does not (only) consist of 2D parcels; 
constructions are illogically divided into parts that 
match with the surface parcels; 
it is needed to store the information of objects with 
every parcel that intersects with the object (e.g. a cable 
for which restrictions need to be registered under 
several parcels): this leads to redundant information 
which is a potential source of inconsistency. 
Management of space under and above the surface will be 
improved when relevant information on real-world objects 
(location, function, geometry) is maintained and can be 
visualised. Besides, a (digital) geographical 3D representation of 
the situation when needed would facilitate the exchange and 
supply of valuable information on the factual situation and a 
better maintainable archive. 
It is important to look at the actual needs of the Kadaster 
concerning 3D situations. These needs depend on the tasks and 
responsibilities of the Kadaster which consist of: 
the registration of the legal status of real estate objects; 
providing information on the legal status of real estate 
objects. 
3D information is not needed in all cases (e.g. rural land). In this 
research a ‘3D cadastral system’ has been defined as a system, 
which gives more insight in the juridical and factual situation 
above and under the surface in case this is relevant with respect 
to the legal security. This insight is obtained through spatially 
defining constructions on, above and under the surface as 3D 
geo-objects in the currently used cadastral system. Whether this 
definition of real-world objects should and will lead to the juridical 
registration of these objects remains beyond the scope of this 
research. 
The approach to combine 2D and 3D data in one geo-DBMS, 
including storage and query, offers the facility to take the juridical 
relevant spatial information in the vertical dimension into account 
when the situation requires this (Stoter and Van Oosterom, 
2000). 
Besides the spatial representation of 3D geo-objects in the 
current geo-DBMS, attributes of these objects will also be 
maintained in the DBMS. The choice of having either implicit or 
explicit relationships (which have to be maintained) between the 
objects above and under the surface with the parcels on the 
surface will complete the incorporation of 3D objects in the 
current cadastral information system. 
The concept of a 3D cadastral registration system is translated 
into prototype implementations. These implementations cover 
the following aspects: 
modelling and storage of 3D geo-objects into a geo-DBMS 
based on 2D parcels (data definitions); 
collecting and preparing 3D data and inserting 
(generalising/converting) the 3D data in the (2D) geo- 
DBMS; 
querying and visualising the data (administrative, 2D, 3D 
and in combination with each other). 
The current database that is used by the Netherlands’ Kadaster 
consists of (Lemmen et al., 1998): 
a geo-database for geometric properties of parcels (and 
buildings for reference purpose) in LKI: Landmeetkundig 
Kartografisch Informatiesysteem ('Information system for 
Surveying and Mapping') 
an administrative database for legal and other 
administrative data related to parcels (AKR: Automatisering 
Kadastrale Registratie: Automated Cadastral Registration) 
Since this research focuses on technical, spatial solutions to 
map the 3D world when the situation requires this, the geo- 
DBMS will be used as starting point. 
3. THE CONCEPT OF A GEO-DBMS 
3. 1 An integrated architecture: the geo-DBMS