J.E. Stoter

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.

Modelling 3D spatial objects in a geo-DBMS using a 3D primitive

The objective of this thesis is answering the following question: How can 3D spatial objects be modelled (i.e. /stored, validated, queried) in a Geo-DBMS using 3D primitives and how can these objects be visualised? To answer this question the theory from various literature is used to create a prototype implementation of a 3D primitive in a Geo-DBMS. 3D Spatial objects are stored with the polyhedron as (3D) primitive. This primitive is easy for users to model objects, can fairly easily be validated, because the algorithms are not too difficult to implement and still result in realistic objects. Each polyhedron has a set of faces, which consist of a set of ordered nodes. These nodes point to a vertex (x,y,x). This means that the data model is geometric with internal topology. Th epolyhedron is stored within the original Oracle Spatial geometry data model. The validation occurs by checking if the polyhedra are stored correctly and after that checking each characteristic of the polyhedra. These characteristics are: flat faces, should bound one volume, simplicit faces and orientable. The improve the performance of queries, a spatial index should be made on a table with polyhedra. The standard Oracle Spatial indices can be used, because of the way the polyhedra are stored in the Oracle Spatial geometry model. A bounding box is constructed around the 3D line or its projection in case of a 2D spatial index. A test shows that it is preferable to create a 3D spatial index (3D R-tree) rather than a 2D spatial index, to get maximal query performance. Using functions that are part of Oracle Spatial, is not suitable for 3D objects, because these functions work with the 2D projection of the 3D objects. Instead, some of the most commonly used functions (e.g. area, volume, point-in-polyhedron and bounding box) are implemented in 3D, so that functions return a realistic value. The polyhedra can be visualised in GIS and CAD programs that can make a DBMS connection. To do this, the polyhedra have to be exported to 3D multi-polygons. This export function is implemented, as is the import function that makes a polyhedron from a 3D multi-polygon. To visualise polyhdra in a VRML viewer, the objects in the database can be exported to a VRML file. This function is implemented, as is the function to make a polyhedron from a VRML object. These concousions together satify the goal to implement a 3D primitive in a Geo-DBMS in a way that improves the maintainability of 3D spatial data and opens the door to more realistic applications.

5D data modelling: full integration of 2D/3D space, time and scale dimensions

This paper proposes an approach for data modelling in five dimensions. Apart from three dimensions for geometrical representation and a fourth dimension for time, we identify scale as fifth dimensional characteristic. Considering scale as an extra dimension of geographic information, fully integrated with the other dimensions, is new. Through a formal definition of geographic data in a conceptual 5D continuum, the data can be handled by one integrated approach assuring consistency across scale and time dimensions. Because the approach is new and challenging, we choose to step-wise studying several combinations of the five dimensions, ultimately resulting in the optimal 5D model. We also propose to apply mathematical theories on multidimensional modelling to well established principles of multidimensional modelling in the geo-information domain. The result is a conceptual full partition of the 3Dspace+time+scale space (i.e. no overlaps, no gaps) realised in a 5D data model implemented in a Database Management System.

Noise mapping and GIS: optimising quality and efficiency of noise effect studies

Abstract Noise caused by industry and infrastructure is a major source of dissatisfaction with the environment in residential areas. In order to assess and monitor the influence of noise, policies on noise control have been developed in most European countries. Noise effect studies are carried out to support these policies. The result of different studies can only be combined or compared if the same indicators for noise exposure and the same assessment methods are used. It is therefore important to develop standardised methods for noise mapping. This is recognised by the DG Environment of the European Commission, who is preparing a Directive on Environmental Noise. This article illustrates and underlines the essence of standardised noise mapping tools. It also describes considerations for the development of these tools and focuses on: accuracy; cost-benefit criteria for noise measures; and presentation of uncertainties in results. Geographical Information Systems (GIS) play an important role in noise mapping. An appropriate use of GIS in mapping noise effects makes it possible to optimise quality and efficiency of noise effect studies. Standardisation will benefit from the possibility of automating the noise mapping process in GIS. Furthermore, GIS can play an important role in estimating and exposing uncertainties.

Towards a 3D cadastre: where do cadastral needs and technical possibilities meet?

Abstract In the Dutch cadastral registration a cadastral object (real-estate object) can be a complete parcel or a condominium right (apartment). The geometries of these legal objects are all based on a planar map which partitions the 2D space. In intensively used areas there is a tendency to use space above and under the surface, e.g. constructions on top of each other, infrastructure above/under the ground, increasing number of cables and pipes, apartments above shops/offices/other apartments. These physical 3D objects cannot be defined as cadastral objects in the cadastral map, which is based on 2D parcels, and cannot be used as a base for registration. From a juridical point of view the current registration is still sufficient in 3D situations. To assure that the Netherlands’ Kadaster is able to address future needs, a prototype of a Land Information System which can handle 3D spatial information is being developed at the Department of Geodesy in collaboration with the Netherlands’ Kadaster. This paper is written as part of the joint research of the Kadaster and the Department of Geodesy. Starting points are the needs of the Netherlands’ Kadaster on the one hand and the technical possibilities on the other hand. In this research a concept is developed in which cadastral needs and technical possibilities meet. The most feasible solution for this is to start with the current 2D cadastre and to extend this with an implementation for the registration of 3D situations. The realisation of this concept is also described in this paper.

3D noise mapping in urban areas

Noise mapping is the process of determining and visualizing noise impact on the environment in order to support environmental policies. Currently most noise impact studies are based on a 2D approach. The 3D output of noise simulation software is processed and visualized in 2D and combined with 2D topographical and other data, such as population distribution, to quantify the effects. The research described in this paper aims at improving visualization and assessment of noise impact on the environment by generating a 3D noise map in cases where 3D effects are relevant. Based on the specific demand, an approach is presented to generate a 3D noise map as a basis for noise impact studies. The proposed concept is proofed by applying it to a sample noise impact study. From experiences with the sample, it can be concluded that the 3D noise map offers significant insight in situations where 3D noise effects are relevant, i.e. in urban areas. Here, current 2D noise maps have limitations. In addition, more accurate assessment of noise impact is possible in particular when different floors of a building close to the noise source and/or behind noise barriers are considered. This paper also elaborates on accuracy aspects in all phases of noise modelling, including a presentation of initial experiments of 3D noise interpolation.

Specifying Map Requirements for Automated Generalization of Topographic Data

Abstract This study aims at acquiring knowledge on map requirements for automated generalization. First, interactively generalized map series were visually analysed together with the specifications that cartographers use to generalize the maps. Second, these map specifications were experimentally implemented on real data in automated processes and compared to an interactively generalized map to see if the results are according to the specifications; to see if the specifications are complete and well-formalized; and to identify situations that were not addressed in the specifications. If required, the specifications were enriched and re-implemented also adding extra information from other sources. The experiments revealed the deep knowledge which cartographers add to the interactive process. Based on this revealed knowledge, recommendations are formulated to specify map requirements for automated generalization of topographic data.

Property in 3D—registration of multiple use of space: current practice in Holland and the need for a 3D cadastre

Abstract A cadastral registration system provides insight in rights and limited rights related to (2D) parcels. In case of multiple use of space, the 2D parcel has shown its limitations. To illustrate this we describe two cases in this article. At our Department a research is carried out in collaboration with the Netherlands Kadaster to study the 3D issue of cadastral registration in a fundamental way. During this research a prototype of a 3D cadastre was developed, in which rights established on 2D parcels can be represented in 3D (3D right-objects). We will give a description of this prototype and will demonstrate that the introduction of 3D right-objects improves the insight in the vertical component of rights considerably by applying this concept to the described cases. Future research will focus on the registration of 3D physical objects (objects as they occur in the real world). The last will require more drastic adjustments in the current cadastral registration system.

Fully automated generalization of a 1:50k map from 1:10k data

This article presents research that implements a fully automated workflow to generalize a 1:50k map from 1:10k data. This is the first time that a complete topographic map has been generalized without any human interaction. More noteworthy is that the resulting map is good enough to replace the existing map. Specifications for the automated process were established as part of this research. Replication of the existing map was not the aim, because feasibility of automated generalization is better when compliance with traditional generalizations rules is loosened and alternate approaches are acceptable. Indeed, users valued the currency and relevancy of geographical information more than complying with all existing cartographic guidelines. The development of the workflow thus started with the creation of a test map with automated generalization operations. The reason for the test map was to show what is technologically possible and to refine the results based on iterative users’ evaluation. The generalization operations (200 in total) containing the relevant algorithms and parameter values were developed and implemented in one model. Particular effort was made to enrich the source data in order to improve the results. The model is context aware which means it is able to apply different algorithms or adjust parameter values in accordance with a specific area. The result of the research is a fully automated generalization workflow that produces a countrywide map at scale 1:50k from 1:10k data in 50 hours. A fully automated workflow may be the only way to produce flexible and on-demand products; consequently, the results were implemented as a new production line in 2013. Issues for further research have been identified.

Challenges for Automated Generalisation at European Mapping Agencies: A Qualitative and Quantitative Analysis

Abstract The automation of generalisation is an important issue at National Mapping Agencies (NMAs) to reduce data production costs and to improve data maintenance. This paper presents the challenges for automated generalisation at European NMAs integrating a qualitative and quantitative analysis. The qualitative analysis focuses on the current strategies for automated generalisation at NMAs. The quantitative analysis extends these findings and measures the status of automated generalisation functionality at NMAs using the required and missing generalisation operators as indicators. The results are interesting for the research community, the software vendors and NMAs to streamline their efforts to accomplish full automation of generalisation processes.