Wilko Quak

The core cadastral domain model

Abstract A standardized core cadastral domain model (CCDM), covering land registration and cadastre in a broad sense (multipurpose cadastre), will serve at least two important goals: (1) Avoid re-inventing and re-implementing the same functionality over and over again, but provide a extensible basis for efficient and effective cadastral system development based on a model driven architecture (MDA), and (2) enable involved parties, both within one country and between different countries, to communicate based on the shared ontology implied by the model. The second goal is very important for creating standardized information services in an international context, where land administration domain semantics have to be shared between countries (in order to enable needed translations). This paper presents an overview of the core cadastral domain model and its developments over the last 4 years. The model has been developed in a set of versions, which were each time adjusted based on the discussions at workshops with international experts and the experience from case studies in several countries of the world (Netherlands, El Salvador, Bolivia, Denmark, Sweden, Portugal, Greece, Australia, Nepal, Egypt, Iceland, and several African and Arab countries). Important conditions during the design of the model were and still are: should cover the common aspects of cadastral registrations all over the world, should be based on the conceptual framework of Cadastre 2014, should follow the international ISO and OGC standards, and at the same time the model should be as simple as possible in order to be useful in practise. Besides presenting the CCDM itself this paper represents an important new wave in geo-information standardization: after the domain independent basic geo-information standards (current series of ISO and OGC standards), the new standards based on specific domains will now be developed. Due to historical differences between countries (and regions) similar domains, such as the cadastral domain, may be modeled differently and therefore non-trivial harmonisation has to be done first. The presented CCDM is a result of this harmonisation and one of the first presented examples of semantic geo-information domain standards. Besides the three well-known concepts, Parcel, Person and Right, at the class level the model also includes immovables such as Building and OtherRegisterObject (geometry of easement, like a right of way, protected region, legal space around utility object, etc.) and the following concepts: SourceDocument such as SurveyDocument or LegalDocument (e.g. deed or title), Responsibilities, Restrictions (defined as Rights by other Person than the one having the ownership Right) and Mortgages. At the attribute level of the model the following aspects are included: SalePrize, UseCode, TaxAmount, Interest, Ranking, Share, Measurements, QualityLabel, LegalSize, EstimatedSize, ComputedSize, TransformationParams, PointCode, and several different date/times. The heart of the model is based on the three classes: (1) RegisterObject (including all kinds of immovables and movables), (2) RRR (right, restriction, responsibility), and (3) Person (natural, non-natural and group). The model supports the temporal aspects of the involved classes and offers several levels of Parcel fuzziness: Parcel (full topology), SpaghettiParcel (only geometry), PointParcel (single point), and TextParcel (no coordinate, just a description). The geometry and topology (2D and 3D) are based on the OGC and ISO/TC211 standard classes. The model is specified in UML class diagrams and it is indicated how this UML model can be converted into and XML schema, which can then be used for actual data exchange in our networked society (interoperability).

The Balance Between Geometry and Topology

The architecture of Geographic Information Systems (GISs) is changing: more and more systems are based on the integrated architecture, i.e. storing geometric data in the Data Base Management System (DBMS) together with administrative data. The first step in building a Geo-DBMS is by having data types and operators for simple features (i.e. geometric primitives): point, line and polygon. This has reached a level of standardisation and is now implemented in several commercial DBMSs. The next step is to have support for the topologically structured features in the DBMS, i.e. complex features. The DBMS can then check and guarantee consistency. In addition, complex operations can be executed within the DBMS. Despite the fact that topologically structured models are well known and that it is not difficult to store the topological references, it still remains an unresolved issue as to how to effectively implement these models within a relational DBMS. In this paper, we describe the design and implementation of a topologically structured management at the DBMS level. Our focus is to translate topological structures into geometric primitives. It is then possible to define a DBMS view on a topological primitive, which makes this appear as a geometric primitive. This process supports the best of both worlds: on the one hand there are advantages of the topological structure (no redundancy) and on the other hand the ease of explicit geometric primitives in querying, analysis and presentation is available.

About Invalid, Valid and Clean Polygons

Spatial models are often based on polygons both in 2D and 3D. Many Geo-ICT products support spatial data types, such as the polygon, based on the OpenGIS ‘simple Features Specification’. OpenGIS and ISO have agreed to harmonize their specifications and standards. In this paper we discuss the relevant aspects related to polygons in these standards and compare several implementations. A quite exhaustive set of test polygons (with holes) has been developed. The test results reveal significant differences in the implementations, which causes interoperability problems. Part of these differences can be explained by different interpretations (definitions) of the OpenGIS and ISO standards (do not have an equal polygon definition). Another part of these differences is due to typical implementation issues, such as alternative methods for handling tolerances. Based on these experiences we propose an unambiguous definition for polygons, which makes polygons again the stable foundation it is supposed to be in spatial modelling and analysis. Valid polygons are well defined, but as they may still cause problems during data transfer, also the concept of (valid) clean polygons is defined.

A storage and transfer efficient data structure for variable scale vector data

This paper deals with efficient data handling of variable scale vector data. Instead of pre-building a collection of data sets on different scales, we create an index structure on the base data set (largest scale data) that enables us to extract a map at exactly the right scale the moment we need it. We present both the classic version of the tGAP (topological Generalized Area Partitioning) data structure for storing our variable scale map, as well as an ameliorated version, both based on topological concepts. We prove that the classic structure needs in a worst case scenario O(e 2) edges (with e the number of edges at largest scale). In practice we observed up to a factor 15 more edges in the variable scale data structure. The tGAP structure has been optimized to reduce geometric redundancy, but the explosion of additional edges is due to the changing topological references. Our main achievement finds its roots in the reduction of the number of edge rows to be stored for the ‘lean’ version (by removing the topological referential redundancy of the classic tGAP), which is beneficial both for storage and transfer. We show that storage space for the data set, plus the index, is less than twice the size of the original data set. The ‘lean’ tGAP, as the classic tGAP, offers true variable scale access to the data and has also improved performance, mainly due to less data communication between server and client.

Generic query tool for spatio-temporal data

Geographical information systems are more and more based on a DBMS with spatial extensions, which is also the case for the system described in this paper. The design and implementation of a generic geographical query tool, a platform for querying multiple spatio-temporal data sets and associated thematic data, is presented. The system is designed to be generic, that is without one specific application in mind. It supports ad-hoc queries covering both the spatial and the thematic part of the data. The generic geographic query tool will be illustrated with spatial and thematic Cadastral data. Special attention will be given to the temporal aspects: a spatio-temporal data model will be described together with a set of views for easy querying. DBMS views play an important role in the architecture of the system: integration of models, aggregation of information, presentation of temporal data, and so on. The current production version of the geographic query tool within the Dutch Cadastre is based on GeoICT products with a relatively small market share (Ingres and GEO++). A new prototype version is being developed using mainstream Geo-ICT products (Oracle and MapInfo). First results and open issues with respect to this prototype are presented.

Construction of the Planar Partition Postal Code Map Based on Cadastral Registration

Accurate postal code maps have many applications within GIS as the postal code has the potential to link the address description of buildings to their location in a specified global reference system in a more natural way. This relationship is possible in both directions: geocoding and reverse-geocoding. These operators demand a mechanism for translating an exact geometric position (i.e. WGS84 coordinate) into a location indication (town, street, house number) and vice versa. As most built-up parcels are provided with a postal code, this indicator can be used as the linkage. This paper describes the procedure, based on the Dutch cadastral registration, to obtain a reliable 6-position (i.e. 2628BX, the highest level of detail possible) planar postal code map for the Netherlands. Problems with existing, Voronoi-diagram based, postal code maps, like intersected houses and arbitrary derived (and thus unrecognizable) boundaries are avoided. The reliability of the derived planar postal code map is discussed and results are illustrated by figures. For a planar coverage, non built-up parcels having no postal code should be assigned a plausible postal code. Furthermore special attention is given to infrastructural parcels. These parcels are divided at their (approximated) skeletons first and then these subdivided infrastructure parcels are piecewise attached to their neighbour parcels. This new approach results in very reliable postal code maps, which are visually attractive too as infrastructure lines can be recognized. The procedure is generic and can be applied to other administrative parcel information as well. The algorithm is implemented using the Computational Geometry Algorithms Library (CGAL), and the possibilities and limitations of this library are addressed as well. Also a number of non-implemented alternatives or improvements are given.

Towards a 3D Feature Overlay through a Tetrahedral Mesh Data Structure

The use of 3D features within GIS has been increasing due to the need to represent, query, manipulate, and analyze man-made objects in relationship to other 3D features related to the surface of the earth. This will yield an increased use of 3D boundary representations of the features. The spatial relationship between two or more features is often evaluated using a geometrical overlay of these features, which reveals whether these features overlap and—if they do—to which extent. We present the design of a 3D overlay algorithm which overlays 3D triangulated boundary representations through a constrained tetrahedral mesh. The intersections between the constrained facets of the 3D features are calculated on the fly and within a restricted neighborhood. We can identify and reconstruct the overlaid parts of the 3D boundary representation within the tetrahedral mesh. The implementation is based on the Computational Geometry Algorithms Library, which proved to have the functionality needed but also has its limitations.

INTERLIS Language for Modelling Legal 3D Spaces and Physical 3D Objects by Including Formalized Implementable Constraints and Meaningful Code Lists

The Land Administration Domain Model (LADM) is one of the first ISO spatial domain standards, and has been proven one of the best candidates for unambiguously representing 3D Rights, Restrictions and Responsibilities. Consequently, multiple LADM-based country profile implementations have been developed since the approval of LADM as an ISO standard; however, there is still a gap for technical implementations. This paper summarizes LADM implementation approaches distilled from relevant publications available to date. Models based on land administration standards do focus on the legal aspects of urban structures; however, the juridical boundaries in 3D are sometimes (partly) bound by the corresponding physical objects, leading to ambiguous situations. To that end, more integrated approaches are being developed at a conceptual level, and it is evident that the evaluation and validation of 3D legal and physical models—both separately and together in the form of an integrated model—is vital. This paper briefly presents the different approaches to legal and physical integration that have been developed in the last decade, while the need for more explicit relationships between legal and physical notions is highlighted. In this regard, recent experience gained from implementing INTERLIS, the Swiss standard that enables land information system communications, in LADM-based country profiles, suggests the possibility of an integrated LADM/INTERLIS approach. Considering semantic interoperability within integrated models, the need for more formal semantics is underlined by introducing formalization of code lists and explicit definition of constraints. Last but not least, the first results of case studies based on the generic LADM/INTERLIS approach are presented.

Towards a high level of semantic harmonisation in the geospatial domain

Abstract Spatial Data Infrastructures (SDIs) aim at making spatial (geographical) data and thus content available for the benefit of the economy and of the society. Agreement and sharing of vocabularies within the SDI are vital for interoperability. But there is a limitation: many vocabularies have been defined within domains while other domains have not been taken into account. Therefore, little harmonisation has been achieved and data sharing between domains within the SDI is problematic. This paper presents a methodology and tools for non-automatic, community driven ontology matching that we developed to harmonise the definition of concepts in domain models that are already being defined and used in operational use cases. Besides the methodology and tools that we developed, we describe our experiences and lessons learned as well as future work.

Construction of the planar partition postal code map based on cadastral reGIStration

Accurate postal code maps could play an important role within GIS as the postal code has the potential to link the address description of buildings and their location in a certain global reference system. This relationship is possible in both directions: address matching and geocoding. These operators demand a certain mechanism in translating an exact geometric position (i.e. WGS84 coordinate) into a location indication (town, street, house number) and vice versa. As most built-up parcels are provided with a postal code this indicator could be used as the linkage. This paper describes the procedure, based on the Dutch cadastral reGIStration, to obtain a reliable 6-position planar postal code map for the Netherlands. Problems with existing postal code maps, like intersecting of houses and arbitrary derived boundaries are avoided.For a planar coverage, non built-up parcels having no assigned postal code should be assigned a plausible postal code. Therefore special attention is given to infrastructural parcels. These parcels are divided at their skeleton first and then piecewise attached to their neighbor parcels. This new approach results in very reliable postal code maps, which are visually attractive too as infrastructure lines can be regognized. The procedure is generic and can be applied to other administrative parcel information as well.The algorithm is implemented using the Computational Geometry Algorithms Library (CGAL), and the possibilities and limitations of this library are addressed as well. The reliability of the derived planar postal code map is discussed and some results are shown by figures. A short overview of alternatives and improvements concludes this paper.