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Many activities wait for 3D solutions in data storage, processing and analysis. Some of the most appealing ones are urban planning, environmental monitoring, telecommunications (mobile services), public rescue operations, real-estate market, utility management. The role of geo-information in all kinds of business processes is increasing as well. Most business transactions rely on information systems, as the geo-information is critical for many of them. Clearly, once the developments in the 3D GIS provide a compatible functionality and performance, spatial information services will evolve into the third dimension. Here, we attempt to summarise the recent advances in 3D GIS development. Introduction Geo-information has already proven its importance for many applications and daily use. A large number of human activities utilise 2D geo-data in some form (paper or digital maps) to complete different tasks. However, the world we are living in is three-dimensional and in many cases the two dimensions are not sufficient. The 3D objects presented as 2D projections may loose some of their properties and relations to other objects and may create difficulties to understand, analyse and evaluate the surrounding world in a critical for a certain activity moment. An increasing number of applications already seek for tools to model, store, analyse and visualise 3D data in an efficient and effective way. Urban (see [11]) and landscape planning, telecommunications, real estate market, 3D cadastre (see [9]), road, railway and building construction, utility management, shopping and tourism are among the most demanding ones. Moreover, maintenance, processing and visualisation of large data sets has been improving progressively in the last decade to approach the current stage when the user can immerse with a 3D model in different levels of mixture between reality and virtuality. Considering the recognised need for 3D data and the high level of technology developments, the "logical" expectation is a variety of software dealing with the third dimension. Unfortunately, the current status of the 3D software market differs. Many vendors develop intensively extensions to their software for more effectively handling 3D data. However, the "killing" software product, capable of dealing with all kinds of 3D data and providing the functionality needed by different application is still missing. The difficulties in devising such a product arise at each stage of the 3D modelling. The paper concentrates on a limited number of those aspects, i.e. structuring and analysis of 3D data. This paper is organised in three parts. The first part concentrates on the last developments in spatial data handling achieved under the OpenGIS specifications. Several experiments demonstrate the current functionality in 3D data maintenance. The second part briefly presents some of the last developments of traditional GIS vendors. The last part discusses research directions. A final discussion summarises the current status and trends and concludes on the future of 3D GIS.
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DDD - “Advances in 3DGIS” Siyka Zlatanova 24
Advances in 3D GIS
Siyka Zlatanova
Section GISt, Delft University of Technology, The Netherlands
s.zlatanova@citg.tudelft.nl
Abstract
Many activities wait for 3D solutions in data storage, processing and analysis. Some of the
most appealing ones are urban planning, environmental monitoring, telecommunications
(mobile services), public rescue operations, real-estate market, utility management. The
role of geo-information in all kinds of business processes is increasing as well. Most
business transactions rely on information systems, as the geo-information is critical for
many of them. Clearly, once the developments in the 3D GIS provide a compatible
functionality and performance, spatial information services will evolve into the third
dimension. Here, we attempt to summarise the recent advances in 3D GIS development.
Introduction
Geo-information has already proven its importance for many applications and daily
use. A large number of human activities utilise 2D geo-data in some form (paper or digital
maps) to complete different tasks. However, the world we are living in is three-dimensional
and in many cases the two dimensions are not sufficient. The 3D objects presented as 2D
projections may loose some of their properties and relations to other objects and may create
difficulties to understand, analyse and evaluate the surrounding world in a critical for a certain
activity moment. An increasing number of applications already seek for tools to model, store,
analyse and visualise 3D data in an efficient and effective way. Urban (see [11]) and
landscape planning, telecommunications, real estate market, 3D cadastre (see [9]), road,
railway and building construction, utility management, shopping and tourism are among the
most demanding ones. Moreover, maintenance, processing and visualisation of large data sets
has been improving progressively in the last decade to approach the current stage when the
user can immerse with a 3D model in different levels of mixture between reality and
virtuality. Considering the recognised need for 3D data and the high level of technology
developments, the “logical” expectation is a variety of software dealing with the third
dimension. Unfortunately, the current status of the 3D software market differs. Many vendors
develop intensively extensions to their software for more effectively handling 3D data.
However, the “killing” software product, capable of dealing with all kinds of 3D data and
providing the functionality needed by different application is still missing. The difficulties in
devising such a product arise at each stage of the 3D modelling. The paper concentrates on a
limited number of those aspects, i.e. structuring and analysis of 3D data.
This paper is organised in three parts. The first part concentrates on the last
developments in spatial data handling achieved under the OpenGIS specifications. Several
experiments demonstrate the current functionality in 3D data maintenance. The second part
briefly presents some of the last developments of traditional GIS vendors. The last part
discusses research directions. A final discussion summarises the current status and trends and
concludes on the future of 3D GIS.
OpenGIS specifications and 3D
The efficient geo-information management (especially when the third dimension is
focussed) is rather complex task requiring high competence in different areas. Several years
ago, leading vendors have decided to stream the efforts in GIS development by founding the
OpenGIS consortium (currently consisting of more than 220 companies, government agencies
and universities). The basic idea is achieving an agreement on the representation, access and
dissemination of spatial information, i.e. the OpenGIS specifications (see [5]). The
DDD - Rivista trimestrale di Disegno Digitale e Design edita da Poli.Design
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DDD - “Advances in 3DGIS” Siyka Zlatanova 25
specifications describing the representation of spatial objects (i.e. the spatial) model are
available in two variants abstract and implementation specifications. The abstract
specifications discuss the conceptual models (already completed) and the implementation
specifications (still at developing stage) provide mechanism for implementation for different
technologies (e.g. SQL, CORBA). According to the OpenGIS specifications, the spatial object
(named geographic feature) is represented by two models, i.e. geometric (i.e. simple feature
specifications, SFS) and topological (i.e. complex feature specifications). While the geometric
model provides direct access to the coordinates of individual objects, the topological model
refers to the composing smaller elements (primitives) and encapsulates some of their spatial
relationships. Suppose the two models are implemented, an application can benefit from the
two representations, e.g. area, volume, distance can be completed on the geometric model,
while analysis based on neighbourhood operations can be performed on the topological
structure. Currently, the implementation focus is toward the geometric model. 3D topological
implementation specifications are not available yet. Many DBMS (Oracle, Ingres, Informix)
offer already maintenance of spatial objects as well as many front-end engines (Microstation,
AutoCAD, ArcGIS) access the spatial data stored in DBMS. Here, we will briefly describe the
implementations by Oracle Spatial and MicroStation GeoGraphics iSpatial.
Geo-DBMS (Oracle Spatial): A spatial objects in Oracle Spatial is defined by the
geometric type. Currently, the supported geometric types are 2D (point, line, polygon) but 3D
coordinates are accepted, i.e. it is possible to describe 3D points, 3D lines and 3D polygons.
Lines and polygons are represented as an ordered set of coordinates (2D or 3D). Self-
intersecting lines are allowed but self-intersecting polygons are not supported. Polygons with
holes are maintained as well. Actually, the geometric type is an object-relational model
(accessible as the standard data types such as integer, date) and contains information about
type, dimension, coordinate system, holes of objects, and provide the list with the coordinates.
Using appropriate coding, it is possible to represent also real 3D spatial objects, e.g. as a set
of polygons or a collection of polygons.
CAD (GeoGraphics iSpatial): In contract to Oracle, the definition of a spatial object
in GeoGraphics cannot be done without specifying the semantic meaning. Three levels of
semantic hierarchy are maintained. Feature represents one or more objects from real world
(e.g. the bank building, the school building). Category groups features with a similar theme
(e.g. buildings, rivers). Finally, project refers to as the root and represents the data for the
entire study area. One project can have many categories but a category may belong to only
one project. To be able to distinguish between different spatial objects stored in Oracle
Spatial, each object has to be assigned to a feature (i.e. its semantics has to be clarified).
Furthermore, edited and newly created objects cannot be posted in the database without
attributing predefined features to them. Spatial layers hold the geometry of the objects, which
actually correspond to geometric types of Oracle Spatial.
Figure 1: The Aula: a building of the TUDelft campus area and the 3D model (left) in
GeoGraphics (right)
DDD - “Advances in 3DGIS” Siyka Zlatanova 26
To investigate the functionality of the two software products in representing,
maintaining and visualising 3D spatial objects, we completed several case studies following
two different approaches. In the fist approach, we had the 3D data organised in Oracle Spatial
in user-defined relational tables and the task was to access, query and edit them from
GeoGraphis iSpatial. In the second approach, the 3D data were available in a DGN file and
had to be imported in geometric structure of Oracle Spatial. The first approach appeared to be
more complex, requiring good skills in both software products. The detailed description of all
the required steps can be found in [12]. The second approach is relatively simple and
straightforward. In both approaches, it was possible to populate, query, visualise and edit 3D
objects. The query can be performed on the basis of the semantic characteristics of the objects
as they are defined in GeoGraphics iSpatial. For example, query on feature “buildings” will
result in visualising all the buildings. If only one feature (e.g. “the Aula”) is attached to only
one spatial object, then this object will be only extracted from the database (see Figure 1).
Figure 2: Query of spatial objects: “Show buildings in a the Vield of View”(left) and “Show
building 17970”(right)
Our experiments have showed that although both packages follow closely the
OpenGIS concepts, still some differences exist. For example, the geometric representation of
Oracle Spatial slightly differs the SFS. Semantic characteristics of a feature are organised in
GeoGraphics iSpatial, as one significant part of the information (semantic hierarchy, links to
geometry types) is maintained at a database level. However, the notations (table names,
columns, object definitions) have very specific application-oriented meaning. If the user
decides to keep the database and change the CAD package, he/she needs to create the feature-
geometry link from scratch.
Real 3D geometric types are missing but the description of 3D data is possible. The Z
value is maintained together with the X,Y values, i.e. it is not an attribute. Although
topological primitives are not implemented yet, Oracle Spatial offers a number of spatial
operations. They operate with X,Y coordinates but some of them accept the Z coordinate as
the computations are still in 2D. We have implemented an operator using the Oracle Spatial
function “with_in_distace” to compute the field_of_view for a given angle and direction of
view. Figure 2, left shows a snapshot with the result of the query. Despite the 3D view the
quesry is completed on the basis of the 2D coordinates.
Apparently the greatest benefits of the DBMS-CAD integration are in the area of
visualisation and editing of data. As frequently commented, the amount of data to be
visualised in 3D increases tremendously and requires supplementary techniques (LOD, on-fly
simplification, etc.) for fast rendering. Having 3D data stored in a database, the user has the
possibility to extract only a limited set of data (e.g. one neighbourhood instead of one town)
and thus critically reduce the time for loading. Locating, editing and examining a particular
object become also quick, simple and convenient. Indeed, the elements that can be edited
correspond to the geometry representation in Oracle Spatial. Figure 2, right shows a building
DDD - “Advances in 3DGIS” Siyka Zlatanova 27
and the wall (the polygon in green) that is accessible for editing. As it can be seen, the face is
a separate polygon, i.e. 3D topology of the building is not preserved.
GIS vendors and 3D
Nowadays, 2D GISs are widely used to handle many spatial issues in a very efficient
manner. However, the same kind of systems fail to operate if more advanced 3D tasks are
demanded. There are already few systems available in the market that can be categorised as
systems providing 3D solutions. We analysed four of them that constitute the largest share of
the GIS market, i.e. ArcView 3D Analyst, (ESRI), Imagine VirtualGIS (ERDAS), GeoMedia
(Integraph Inc.) and Geomatica (PCIGeomatics). The results are reported in [12]. Here I will
give a short summary. All the systems provide excellent tools for 3D visualisation, animation
and navigation through 3D textured models (Figure 3). Imagive Virtual GIS offers two
interesting 3D visualisation features. The system allows the user to include and visualise 3D
models (e.g. 3D models of trees in a forest area) in a selected polygon or along a line in an
easy and convenient way (and thus largely increase the realism). A logo layer is introduced
that can accommodate 2D image into the 3D scene and stretch it over the entire view as
foreground (e.g. cockpit in a fly animation, Figure 3, right). Most of them offer sufficient
tools to manipulate 2.5D data such as surface generation, volume computation, draping
images, terrain inter-visibility, etc. Access to data distributed on different servers is also
greatly improved. All the systems revealed little provision of 3D GIS functionality in terms of
3D structuring, 3D manipulation and 3D analysis. The full 3D geometry (the z-coordinate is
basically an attribute), 3D topological relationships and 3D analysis are still areas to be
entered by the general-purpose GIS vendor.
Figure 3: ArcScene, ESRI (left), TerraBuilder (middle) and Imagine VirtualGIS, ERDAS (right)
Research in 3D GIS
The research in 3D GIS is intensive and covers all aspects of the collecting, storing
and analysing real world. 3D analysis and the related issues (topological models, frameworks
for representing spatial relationships, 3D visualisation) are mostly in the focus of
investigations. The 3D topological model is the key issue, since it is related to the
representation of a large group of spatial relationships, e.g. inclusion, adjacency, equality,
direction, intersection, connectivity. As it was mentioned above, OpenGIS consortium has not
achieved a consensus on 3D topological implementation specifications. The problems with
the third dimension are many more. For example, the well known relationship between arc
and face, i.e. an arc has two neighbouring faces (i.e. left and right), is not valid in the 3D
space (i.e. one arc can have several neighbouring faces)
A large number of 3D models are reported in the literature, but the research
concentrates around few basic ideas, as the level of explicitly described spatial relationships
varies. Few examples follow. Molenaar [4] presents a 3D topological model called 3D Formal
Vector Data Structure (3DFDS). The model is the first that takes into account semantic and
geometric characteristics of spatial object. Nodes, arcs, edges and faces describe the four
basic feature types named points, lines, surfaces and bodies. The model has been used by
DDD - “Advances in 3DGIS” Siyka Zlatanova 28
many for describing spatial objects in DBMS or objects-oriented implementations. Abdul-
Rahman [1] presents an object-oriented implementation on the Molenaar’s data model. Work
by Pilouk [7] focuses on the use of Tetrahedron Network (TEN), maintaining triangles,
tetrahedrons, arcs and nodes to describe spatial objects. Zlatanova [10] discusses some
aspects of the data structuring and 3D visualisation with respect to data query over the Web.
The proposed data structure lacks arcs in order to improve the performance of the system.
The Urban Data Model (see [3]) represents the geometry of a body or a surface by triangles as
each triangle is defined by a set of nodes. More examples of 3D topological models can be
found in [13]
It is rather difficult to give priorities to only one 3D topological model. Advantages of
a topological model in one aspect may occur as disadvantages in another aspect. For example,
the arbitrary number of nodes per face (3DFDS, SSS) can be seen as advantage and
disadvantage for different applications. It is very convenient for modelling complex 3D
objects (e.g. buildings) since an inappropriate partitioning (from user point of view) is not
necessary. However, the same freedom in face description may lead to problems in
visualisation (the rendering engines handle only triangles). Furthermore, the operators for
consistency check may become very complex. Due to the omission of arcs, data structures
(SSS, UDM) can benefit form the significantly faster data traverse. However, navigating
through surfaces (e.g. “follow shortest path”) may become time-consuming. Representing
bodies as a set of faces (e.g. SSS) yields advantages for extracting the coordinates of the
objects, but navigation queries might be disturbed since the co-boundary relationships (i.e.
face-body) is not maintained. Bearing in mind the large variety of topological models (also the
implemented in 2D systems), a possible solution could be the maintenance of topological
models in a metadata table (in DBMS) and a supplementary set of rules can provide a
consistent conversion between them (see [6]).
Mechanisms for representing spatial relationships are yet another “hot area” of
investigation. OpenGIS consortium has adopted two frameworks known as Egenhofer
operators and Clementini operators based on the 9-intersection model (see [5]). Although the
topology is considered the most appropriate mechanism to describe spatial relationships, the
study on applicability of other mathematical frameworks continues (see [2]).
Another significant area of 3D GIS research is devoted to Web applications. The Web
has already shown a great potential in improving accessibility to 2D spatial information
(raster or vector maps) hosted in different computer systems over the Internet. The first
attempt to disseminate and explore 3D data, i.e. VRML, appeared to be rather “heavy” for
encoding real geo-data due to the lack of a successful compression concept. Despite the
drawbacks, the language became a tool for research visualisation. Researchers could
concentrate on data structuring and analysis and leave the rendering issues to VR browsers
offered freely on Internet. GeoVRML (VRML extended with geo-nodes) and Geographic
Modelling language (GML) are another promising opportunities for representing 3D data on
the Web. Based on XML concepts, GML provides larger freedom, flexibility and operability
than VRML.
Discussion
The study on current implementations of OpenGIS specifications displayed that
DBMS&CAD&GIS developers have rapidly adopted the idea of common standards. The first
step is made, i.e. DBMS support spatial objects and many front-end engines make use of it.
The performance of the DBMS (in maintenance of spatial objects) is already quite good and
continues to improve with each new release (see [8]). The third dimension with respect to
topological issues is still in the hands of the researchers. While quite many 3D topological
models are reported in the literature, 3D spatial operations and analysis still have to be
DDD - “Advances in 3DGIS” Siyka Zlatanova 29
addressed by the researchers. 3D buffering, 3D shortest route, 3D inter-visibilities are some of
the most appealing for investigations.
The 3D progress in traditional GIS packages is great but mainly in the area of data
presentation and surface analysis. The models are still 2D and the Z coordinate is maintained
as an attribute.
3D GIS requires appropriate means not only for visualising and exploring 3D textured
models but also for building and storing them. Observations on the demand for 3D City
models show user preferences for photo-true texturing. Currently, a limited number of
packages offer means for mapping images onto geometry (e.g. facades). Trading photo-true
texture requires a variety of topics to be considered, e.g. standardisation of parameters for
image-geometry references and image organisation at a database level.
Despite the variety of issues waiting for an appropriate solution, the recent advances in
geo-processing change the understanding of GIS. Instead of a monolith, desktop, individual
system, GIS is becoming an integration of strong database management (ensuring data
consistency and user control) and powerful editing and visualisation environment (inheriting
advanced computer graphics achievements).
References
[1] Abdul-Rahman, A., 2000. The design and implementation of two and three-dimensional triangular irregular
network (TIN) based GIS, PhD thesis, University of Glasgow, Scotland, United Kingdom, 250 p.
[2] Billen R., S. Zlatanova, P. Mathonet and F. Boniver, 2002, The Dimensional Model: a framework to
distinguish spatial relationships, in: Advances in Spatial Data handling, D.Richardson, P.van Oosterom (Eds.),
Springer, Ottawa, Canada, 9-12 July, pp. 285-298
[3] Coors, V., 2002, 3D GIS in Networking environments, CEUS (to be published), 17 p.
[4] Molenaar, M., 1990, A formal data structure for 3D vector maps, in: Proceedings of EGIS’90, Vol. 2,
Amsterdam, The Netherlands, pp. 770-781
[5] Open GIS Consortium, Inc., 1999, The OpenGIS abstract specification, topic 1: Feature geometry. Technical
Report Version 4 (99-101.doc), OGC, URL: http://www.opengis.org/techno/abstract.htm
[6] Oosterom. P.J.M. van, J.E. Stoter, S. Zlatanova, W.C. Quak, 2002, The balance between Geometry and
Topology, Advances in Spatial Data handling, D.Richardson, P.van Oosterom (Eds.), Ottawa, Canada, 9-12 July
[7] Pilouk, M., 1996, Integrated modelling for 3D GIS, PhD thesis, ITC, The Netherlands
[8] Quak, W., P. Oosterom and T. Tijssen, 2002, Testing current DBMS products with realistic spatial data, in:
Proceedings of the 5th AGILE conference on Geographic Information Science, ISBN 84-7632-734-X, 25-27
April, Palma de Mallorca, Spain, pp. 189-194
[9] Stoter J.E., 2002, 3D Cadastres, state of the art: from 2D parcels to 3D registrations, GIM International, the
world magazine for Geomatics, February, 2002.
[10] Zlatanova, S., 2000, 3D GIS for Urban development, PhD thesis, ITC, The Netherlands, 222 p.
[11] Zlatanova, S. and T. Bandrova, 1998, User requirements for the third dimensionality, E-mail seminar of
Cartography 1998: Maps of the future, Vol. 1, Sofia, pp. 61-72
[12] Zlatanova, S., A.A. Rahman and M.Pilouk, 2002, 3D GIS: current status and perspectives, in Proceedings
of the Joint Conference on Geo-spatial theory, Processing and Applications, 8-12 July, Ottawa, Canada, 6p.
CDROM.
[13] Zlatanova, S. A.A. Rahman, and W. Shi, Topology for 3D spatial objects, Journal of Geospatial
Engineering (in press).
Siyka Zlatanova is a researcher at the GISt section, Delft University of Technology,
The Netherlands (since 2000). She has graduated as a surveyor at the University of
Architecture, Civil Engineering and Geodesy (UACG), Sofia, Bulgaria in 1983 and
has obtained her PhD degree on 3D GIS for urban modelling at the Graz University
of Technology, Austria in 2000. She worked as a software programmer at the Central
Cadastre in Sofia, Bulgaria (1984-1989), an assistant-professor at UACG, Sofia,
Bulgaria (1989-1995) and a researcher at the Institute of International Institute for
Geo-information Science and Earth Observations (ITC), The Netherlands (1995-
1999). Her interests are in 3D GIS: 3D reconstruction, 3D data structures, 3D spatial
analysis and 3D visualisation.
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................. Full PhD Thesis availble at: http://zlatanova.xyz/PhDthesis/............................. ------------------------------------------------------------------------------------------------------------------------------------------- The growth of cities has complicated the tasks of urban planners and managers to such an extent that new solutions are needed for maintenance and analysis of data. The most challenging issue, i.e. the handling of 3D geo-information, has been investigated for years and has resulted in various concepts and software developments. The work reported, however, reveals little evidence of the integration of concepts on 3D data structuring to enable spatial analysis and ensure fast 3D visualisation. The goal of this research is the definition of a conceptual model that is capable of handling the variety of objects of interest for urban planners in a way appropriate to analysis and interactive 3D visualisation employing current technology developments. Bearing in mind the increasing publicity surrounding planning and management activities, the research concentrates on a web-oriented approach to access and 3D visualisation. To achieve this goal, the research strategy followed is: 1) investigating and classifying objects of interest, 2) specifying a web oriented system architecture for query, retrieval and 3D visualisation, 3) defining a 3D GIS model and 4) implementing and testing. An investigation into user requirements for 3D GIS is completed on the basis of information currently maintained in a representative municipality and the interview of producers of urban data. A system architecture for web query and 3D visualisation based on a DBMS, a Web server, Web browsers and VR browsers is suggested and implemented. The client-server communication relies on CGI scripts. VRML and HTML are employed to develop a front-end user interface. An extended definition of an object is presented in order to handle objects, their characteristics, behaviour and 3D topological relationships. Considering user and visualisation requirements, a 3D topological model called the Simplified Spatial Model is formally defined using set theory notions. The model maintains the four geometric abstractions of a real object, i.e. point, line, surface and body, which are formed by two constructive objects, i.e. node and face. The spatial model (holding information about geometric description and spatial relationships) and two spatial object's components (geometric attributes and geometric behaviour) are organised in a Simplified Spatial Schema and implemented in an RDBMS. Links to existent data collection procedures are explored and adapted to provide data for functional tests. The capacity of the model to derive 3D topological relations is proven by an elaborated investigation on the basis of the intersections between boundary, interior and exterior of an object. The suitability of the model for web query and 3D visualisation is proven by tests on representative spatial queries executed on a prototype system. The flexibility of the user interface suggested is demonstrated by a number of examples. The theoretical and experimental work carried out accomplishes the goal of the research: a 3D GIS model is defined to maintain data about thematic and geometric characteristics, behaviour and relationships (3D topology) between objects, ensuring quick realistic 3D visualisation. Moreover, the results of the research contribute to: 1) the clarification of the possible 3D topological relations between spatial objects, 2) the query and visualisation of 3D spatial data over the Web and 3) the creation of realistic 3D models.
Article
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Topology is one of the mechanisms to describe relationships between spatial objects and thus the basics for many spatial operations. In this paper, we present models that are built on the topological properties of the spatial objects. They are usually called topological models and are considered by many the best suited for complex spatial analysis (i.e. shortest path, line of view). There are a number of topological models that are utilized for 2D and 2.5D spatial objects by experimental and commercial software. However, when we move to the next dimension (i.e. 3D), many difficulties are encountered in establishing the topology for the objects (consisting of points, lines, faces, and solids). This paper describes some existing topological models and a comparison between them is made. The advantages and disadvantages of the models and the recent experiments by the authors towards formalizing a 3D topology for 3D objects is discussed. The paper considers the models in object-oriented (OO) environment as well. Finally, we summarise the application of the 3D topological model, highlight the current approaches and the outlook of the works.
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Currently, variety of software is already capable of handling a wide range of spatial problems, beginning with approaches for describing spatial objects to quite complex analysis and 3D visualisation. However, increasing number of applications need more advanced tools for representing and analysing the 3D world. Among all types of systems dealing with spatial information, GIS has proven to be the most sophisticated system that operates with the largest scope of objects (spatial and semantic), relationships and provide means to analyse them. However, what is the status of the 3D GIS? It is the aim of this paper to find the answer by analysing both software available and efforts of researchers. An overview of several commercial systems and a 3D case study performed in Oracle and Microstation provides knowledge about the 3D functionality offered by commercial systems. The most significant achievements in the 3D research area concerning key issues of 3D GIS, i.e. 3D structuring and 3D topology portray the current research status. At the end, the paper addresses some of the issues and problems involved in developing such a system and recommends directions for further research. The scope of the paper is limited to 3D GIS systems and research in vector domain. Problems of subsurface applications are excluded as well.
Article
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It has long been realised in the GIS community that most 2D GISs are capable of handling 2D spatial data efficiently, but systems have had less success with 3D spatial data. This is reflected in the current GIS market place where systems which can handle 3D data are hardly available - due to several impediments in implementing suchsystems. This thesis attempts to address some of the impediments. The impediments which relate to spatial data especially data representation, data structuring and datamodelling using object-oriented (OO) techniques are the foci of this thesis. OO techniques are utilized because they offer several advantages over the traditional (i.e.structural) techniques in software development. In the aspect of spatial representation, several major representations are investigated, which then lead to identifying anappropriate representation both for 2D and 3D data, that is triangular irregular network (TIN) data structures. 2D data is represented by a 2D TIN, and 3D data is represented by a 3D TIN (also called a tetrahedral network or TEN). Several algorithms were developed for the construction of the data structures where procedures such as distance transformation (DT) and Voronoi tessellations were utilized. Besides standard Delaunay triangulations, constrained triangulations were also developed, thus the inclusion of real world objects in the spatial data modelling can be facilitated. Four classes of real world objects are identified (i.e., point, line, surface, and solid objects). For the purpose Abstract ii of spatial data modelling of the four types of objects, a formal data structure (FDS) is utilized. An OO database development is also investigated. This is done via a commercial system called POET OO DBMS where spatial data query and retrieval can be performed. Further, two application programs are developed, namely contouring and volume computation. All the developed algorithms and methods were tested using real data sets. To facilitate the output of the developed methods and algorithms, software called TinSoft, which is a Windows-based Multiple Document Interface software was developed in this research.
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Support of spatial data types can be found in more and more commercial Database Management Systems (DBMSs). In our research we have tested three DBMSs with support for spatial data: Oracle, Informix and Ingres. Both the functionality, a predefined set of questions had to be translated into spatial SQL queries and the performance is evaluated. In order to test the performance a cadastral data set, including a boundary table with more than 10.000.000 variable length rows, has been used.
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A unique characteristic of GIS as compared to other information systems, is their capacity to manage spatial relationships, such as connections or interrelations among objects in the geometric domain. A number of frameworks use topology as a basic mechanism to define spatial relationships. The OpenGIS consortium has adopted one of them, i.e. the 9-intersection model. In this paper, a new framework for representing spatial relationships - the Dimensional model - is introduced. The model was first developed for convex spatial objects and is now extended to topological n-manifolds. It is based on two major concepts, i.e. the dimensional elements of spatial objects and the dimensional relationships, i.e. the relationships existing between dimensional elements. The model addresses a substantial group of spatial relationships and provides a flexible framework to consider either
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In this paper, we present a data model for 3D geometry and topology in a 3D-GIS. This data model includes the concept of multiple representations for the same feature. Together with a spatial index, these multiple representations will be used to visualize the 3D-GIS data in a distributed networking environment. The data model and the progressive transmission is tested with an area-wide city model of Darmstadt.
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A three dimensional (3D) model facilitates the study of the real world objects it represents. A geoinformation system (GIS) should exploit the 3D model in a digital form as a basis for answering questions pertaining to aspects of the real world. With respect to the earth sciences, different kinds of objects of reality can be realized. These objects are components of the reality under study. At the present state-of-the-art different realizations are usually situated in separate systems or subsystems. This separation results in redundancy and uncertainty when different components sharing some common aspects are combined. Relationships between different kinds of objects, or between components of an object, cannot be represented adequately. This thesis aims at the integration of those components sharing some common aspects in one 3D model. This integration brings related components together, minimizes redundancy and uncertainty. Since the model should permit not only the representation of known aspects of reality, but also the derivation of information from the existing representation, the design of the model is constrained so as to afford these capabilities. The tessellation of space by the network of simplest geometry, the simplicial network, is proposed as a solution. The known aspects of the reality can be embedded in the simplicial network without degrading their quality. The model provides finite spatial units useful for the representation of objects. Relationships between objects can also be expressed through components of these spatial units which at the same time facilitate various computations and the derivation of information implicitly available in the model. Since the simplicial network is based on concepts in geoinformation science and in mathematics, its design can be generalized for n-dimensions. The networks of different dimension are said to be compatible, which enables the incorporation of a simplicial network of a lower dimension into another simplicial network of a higher dimension.The complexity of the 3D model fulfilling the requirements listed calls for a suitable construction method. The thesis presents a simple way to construct the model. The raster technique is used for the formation of the simplicial network embedding the representation of the known aspects of reality as constraints. The prototype implementation in a software package, ISNAP, demonstrates the simplicial network's construction and use. The simplicial network can facilitate spatial and non spatial queries, computations, and 2D and 3D visualizations. The experimental tests using different kinds of data sets show that the simplicial network can be used to represent real world objects in different dimensionalities. Operations traditionally requiring different systems and spatial models can be carried out in one system using one model as a basis. This possibility makes the GIS more powerful and easy to use.
The OpenGIS abstract specification, topic 1: Feature geometry
  • Open Gis Consortium
  • Inc
Open GIS Consortium, Inc., 1999, The OpenGIS abstract specification, topic 1: Feature geometry. Technical Report Version 4 (99-101.doc), OGC, URL: http://www.opengis.org/techno/abstract.htm