=Paper=
{{Paper
|id=Vol-176/paper-10
|storemode=property
|title=GeKon - Applying Novel Approaches to GIS Development
|pdfUrl=https://ceur-ws.org/Vol-176/paper14.pdf
|volume=Vol-176
|dblpUrl=https://dblp.org/rec/conf/dateso/Richta06
}}
==GeKon - Applying Novel Approaches to GIS Development==
https://ceur-ws.org/Vol-176/paper14.pdf
GeKon -– applying
GeKon Applyinga Novel ApproachestotoGIS
novel approaches GIS
Development
development
Tomas
TomášRichta
Richta
Department
Department of
of Computer
ComputerScience,
Science,FEE,
FEE,CTU
CTU- -Czech
CzechTechnical
TechnicalUniversity
UniversityininPrague,
Prague,
Karlovo nam.
Karlovo 13, 13,
nám. 70870833, 33,
121121
35 Prague 2, The
35 Prague CzechRepublic
2, Czech Republic
richtt1@fel.cvut.cz
richtt1@fel.cvut.cz
Abstract. This paper describes a few ideas concerned with geograph-
ical information systems (GIS) development. Those ideas come from a
GIS development project named GeKon, which is now held on the De-
partment of Computer Science at CTU. The first of them deals with a
huge semantic gap between the complex structure of real world and its
representation in GIS. Some papers describe this problem as a conse-
quence of wide usage of procedural programing languages and relational
database management systems in contemporary GIS development. The
object-oriented approach is usually recommended as a better way of con-
structing such systems. We demonstrate here our findings in object mod-
elling, programing and data management achieved in GeKon project.
The other idea shows the fact, that not always the term object-oriented
is understood in the same way. People usually have in mind some spe-
cific programing language and its structures, instead of the real problem
and its solution. In this paper we want to clarify those misleadings and
try to describe requirements, that should be fulfilled to achieve expected
benefits of this approach. We also introduce next supposed steps in the
GeKon project.
Keywords: GIS, semantic gap, object-orientation, data modelling, Smalltalk, OODBMS
1 Introduction
At the beginning, we have to slightly describe geographical information systems
(GIS) evolution process to reader be more familiar with questions connected with
this area of research. Present GIS were principally constructed as tools for com-
puter based maintenance of geo-referenced data formerly kept in cartographical
tools, like maps, atlases, cadastral plans, etc. Evolution of such systems probably
started with the idea of cartography digitalization drawn ahead by the vision of
map producing acceleration, and also faster access to carographical data, includ-
ing sorting, searching, and other functions that could lead to better utilization
of geo-referenced data.
V. Snášel, K. Richta, J. Pokorný (Eds.): Dateso 2006, pp. 95–102, ISBN 80-248-1025-5.
96 Tomáš Richta
1.1 Present GIS data management
Present problems of GIS systems have probably their origin in the way of GIS
data production. The process of cartography digitalization consists of scanning
cartographical tool, and then its vectorization by laying vector paths over the
lines in the map. The data produced by this process tend to come under three
main geometry types:
– spotted, when some interesting spot had been captured, like a church, a tree,
a well, etc.
– linear, when some linear data had been captured, like roads, borders, rail-
ways, networks, etc.
– planar, where some area of interest had been captured, like cadastre area,
city district, etc.
This separation lead to three main data types used in present GIS: points,
lines and polygons. Almost all such systems use as its storage device those three
elements. One of the first companies in GIS field named ESRI had invented
special file format named shapefile (SHP) for storing these data. SHP becomes
something like a standard in GIS data management. Probably for better preser-
vation of cartographical information, data were collected separately in thematic
parts. It means, that all churches in observed area were vectorized in one point-
based shapefile, all roads in one line-based shapefile, etc. This approach lead
to very discrete representation of real world. When the map is to be retrospec-
tively reconstructed in GIS, all thematic files has to be layered over themselves
to obtain proper cartographical representation. Layers are not connected among
themselves, so ie. the information about roads leading to a well is not present.
Further needs of additional information capturing and storage lead to ex-
tension of shape format with so called attribute data component like names,
numbers, etc. At the same time as this problem arose, the relational approach
to data management achieved great concern. So the GIS files were extended
with database file (DBF) including attribute data, connected to their geometry
representation in shapefiles. Both those files were stored separately. Relational
tables consist of domains, and records, so the real world information has to be
separated and simplified into these parts to be stored in DBF. This approach
also lead to more discrete GIS data quality and omitting of more complicated
information.
Both stated approaches have not changed since the beginning of GIS. The
only novel approach is to store SHP and DBF files into relational database
management system and reach them through the SQL. But this way only leads
to bigger conservation of the problem.
1.2 Semantic gap
Wikipedia describes semantic gap as a mismatch caused by some conflicts emerg-
ing in layered systems, when a high level of abstraction need to be translated
GeKon – Applying Novel Approaches to GIS Development 97
to lower, more concrete artifacts [1]. When we try to imagine our modern infor-
matical world as a very complex layered system, we see the real world structure,
semantics, and topology on one side and its computer based representation in
information systems on the other side. Between them, there are multiple sensors,
but not only mechanic ones, but also human senses as a main set of tools used
in present digitalization process. Rapant defines the term of geoinformatics as
a scientific discipline dealing with quality, behavior, and reciprocal interactions
of spatial objects, phenomena, and processes by force of their digital models
combined with information technologies [2]. When a GIS may be able to serve
as a tool for better understanding of the real world, its way of storing real data
must be as natural as possible. But present GIS with their fragmented data
model, layered representation, and relational simplicity are not able to provide
it. For example, when we want to describe a village, we need to prepare a number
of layers covering all fields of our interest, ie. buildings, roads, fields, gardens,
forests, sewages, electrical wring, gas pipelines, churches, wells, pubs, shops, bus
stations, etc. For each theme, we need a relational table blueprint that describes
whether there are points, lines, or polygons, and what attributes we want to
store along with geometry. This leads to strenuous process of uniformization of
gathered information and quanta of discrete data production. All houses must be
described by the same group of attributes, and the information whether house
is a pub is stored somewhere else, than the number of its stories. Also when
we want to combine together villages belonging to some administrative area, we
need to flatten out all the villages thematic layers to be coherent and thus com-
parable together. This process isn’t very natural and its results do not exactly
cover described original. And that is why the semantic gap emerges.
2 Object-oriented approach
Merunka recommends an object-oriented approach (OOA) as a good solution of
semantic gap in information systems development [3]. He states that OOA solves
this problem by introducing the idea of higher level of abstraction in software
development with emphasis on modularity, reusability, and standardization. He
also summarizes main criteria of object-oriented system:
1. Data and its functionality are encapsulated in one logical entity, which is
called object.
2. Objects communicate by sending messages to each other.
3. Objects are able to inherit their properties from other objects.
4. Objects are collected in classes together with other similar objects.
5. Different objects are able to react to the same message, which is called
polymorphism.
6. Objects could also have other relationships like composing, dependency, or
delegation.
7. Methods are programs consisting of operations over object data. Methods
are components of objects.
98 Tomáš Richta
8. Object identity is independent on object data.
Comparing OOA ideas with GIS problems gives a new horizon to their so-
lution. Our natural way of perception of material aspect of the real world is
that everything is an object, and now with OOA everything is possible to be
an object in our computer memory. What we only need is to start using OOA
in instant. No more thinking about geometrical representation of objects or the
way how to store them into tables.
Of course, this is not the novel idea. Mitrovic and Djordjevic-Kajan described
in 1996 OOA as natural paradigm for highly complex domains, especially be-
cause it maintains a direct correspondence between real world and application
objects [4]. Kofler in in 1998 in his PhD. thesis about large 3D GIS databases
recommended OOA as an obvious choice for any new GIS [5]. Chance et al.,
key developers of GE Smallworld GIS, describe OOA as highly effective when
applied to the requirements of GIS [6]. The question may arise, why nothing
has changed yet, even if those articles had already been written within past ten
years.
2.1 Object-oriented modelling
Looking for some indications of OOA emerging in GIS, we could find a few
papers describing object modelling in GIS, especially when the 3rd dimension
has to be introduced to those systems. For example, Nebiker wrote in 2003 about
his fully object-oriented model for 3D geo-objects [7]. Also Kolbe and Groeger
work on their unified standard for 3D city models that is strictly based on OOA
[8].
2.2 GIS development projects
There are also some projects, that have already implemented parts of GIS using
OOA. One of them is already cited in Koflers PhD. thesis [5] where he described
a few tests of GIS database implemented over two examples of object-oriented
database management systems - ObjectStore and O2. Kofler used as a platform
SGI Indigo workstations with MIPS R4400 CPU at 250 MHz and 128 Mbyte
main memory, which is not very strong but it is adequate to the year of publish-
ing. He states that OODBMS has bigger performance demands than traditional
file systems, but still recommends them as a best solution for GIS database.
Balovnev et al. implemented software for 3D/4D geo-scientific applications
developement named GeoToolKit [9]. They used C++ and ObjectStore as core
technology tools. GeoToolKit is a class library for the storage and retrieval of
spatial objects within an object-oriented database. Developers state that their
approach lead to separation of focus on the geoapplication semantics and the
need of spatial objects assembly from multiple relational tables. They also men-
tion the reduction of the code written, improvement of its understandability,
and they descibe some interesting applications implemented with the use of
GeoToolKit library.
GeKon – Applying Novel Approaches to GIS Development 99
One of the other projects is GeoViewer implemented by Lurie et al. in 1997
[10]. Its an object-oriented GIS framework with optimized spatial geometry rep-
resentation providing transparent linkage to data objects. GeoViewer is written
in Smalltalk with small amount coded in C. Minimal documented configura-
tion for running GeoViewer is Sun Sparc 10 with 64MB of RAM or Pentium
166 with 64MB of RAM. This project is remarkable because it incorporates our
main ideas about design of GIS, such modelling natural relationships between
the geodata, or independent representation of objects and its geometric repre-
sentation. Taking the year of publication into account, the measure of innovation
ideas is stunning. Also the question arises, why this is not the main approach in
nowadays GIS.
2.3 GeKon project
Because we see all of those projects very important as a way to improve present
GIS applications, we have also opened research project concerning OOA used
in GIS development. The name of this project is GeKon an it was started as
a semestral work in one of our Software engineering courses. Members of the
development team were three undergraduate students - Ivo Kondapaneni, Petr
Novosad, Jiri Verunek, and author himself. Ivo Kondapaneni had to leave our
project later for his other academic duties, so project extent had to be partially
narrowed.
GeKon system is now able to load data from shapefiles and display it on the
computer screen. It is also possible to zoom displayed data and move over it. As
a test case the city GIS problem was chosen and as a development platform we
used Squeak Smalltalk dialect. In Fig. 1. we introduce our object model.
This model shows the GeKon structure - space subdivision, geometry and
city object model. In the space subdivision part we formed our idea that it was
necessary to maintain some sophisticated indexed structure that allowed fast
searching. We use two trees here. First one is responsible for logical subdivision
of the city (city districts, basic settlement units, and counting districts) and
it is implemented with collections. Second one is responsible for searching the
physical space within the counting district and it is implemented as a R-tree.
Loaded objects are primarily classified according to the logical space subdivision
and then inserted into R-tree of relevant counting district.
Geometry part of our model is responsible only for the geometric represen-
tation of objects. Now it contains only necessary representations - point, line
and polygon, expanded with 3D solid representations. Each shape has its own
bounding box which is stored in space subdivision structures.
The logical object structure of city is the only demonstrative example of
part of the city configuration. Its main purpose is to show how we need to model
the reality - naturally. We expect that in the future this part of the GIS will be
constructed in some visual metamodeller directly by the GIS user at the moment
of data import. This approach assumes strict clear disjunction of the data and
its representation.
100 Tomáš Richta
Fig. 1. GeKon object model
Visualization was partly implemented using OpenGL, but after loss of I. Kon-
dapaneni we had to choose easier way. So we used Squeak morphic visualization
system, which is sufficient, but lacks possibilities to improve graphics perfor-
mance in the future like redrawing using textures etc. So we plan to redevelop
OpenGL rendering engine for GeKon in future.
Data management has not been covered yet, we are storing all data in
Smalltalk image. In future, we plan to incorporate OmniBase as a database
management system, which ensures native storage and retrieval of objects. We
also plan to cooperate with another project held on our department named Cell-
Store, which deals with heterogeneous data storage and now serves as native
XML database.
During the development we used sample data from the ICIP (Institute of City
Informatics - Prague), covering the Josefov city district. The average loading
time was 1749ms per 1MB and the refreshing time about 320ms, which is not
bad. But we see these results orientational only, because the sample is too small
to give evidence of the GeKon capabilities. Further we want to use bigger data
collections for testing, but they were not available at the moment.
GeKon – Applying Novel Approaches to GIS Development 101
3 Conclusion and future work
In this paper we described semantic gap problem between the real world and
its computer based representation. This problem was described from the GIS
point of view. GIS are still very tightly coupled with the old fashioned represen-
tation of the real world by using files and relational tables. We discussed here
OOA as one of the approaches that are able to overcome semantic gap. Some
interesting projects concerning object modelling and object-oriented implemen-
tations of GIS systems were slightly introduced. In the end of our paper, we
also presented our own project GeKon, in which we developed the prototype of
object-oriented GIS. Now we want to summarize discovered requirements for the
GIS development and also planned work in the GeKon project.
3.1 GIS development requirements
Based on our experience in GeKon system development and also on the knowl-
edge from previously cited papers we strongly recommend following rules to be
applied in OOA GIS development:
– Separate geometric representation from object itself to be independent on
its shape.
– Use R-trees or other indexing structures for fast searching in space and
efficient data retrieval.
– Pay attention to very fast rendering algorithms to prepare the most com-
fortable environment for users.
– Use metamodeller controlled by the user to obtain the logical structure of
the place of interest.
– Use strictly pure non-hybrid object-oriented language to avoid programmers
cheating (for details see [3]).
3.2 Further steps in GeKon project
In future, we want to continue in development of GeKon system on our depart-
ment, partly in the form of dissertation, diploma and other thesis, partly as
student semestral projects. Fig. 2. describes the roadmap of planned work.
References
1. Wikipedia, the free encyclopedia, encyclopedia, www.wikipedia.org.
2. Rapant P.: Zaklady geoinformatiky I. (Geoinformatics fundamentals I.), course
lecture, Ostrava, The Czech Republic, 2005.
3. Merunka V.: Objektove orientovany pristup k projektovani informacnich systemu
(Object oriented approach to information systems development), habilitation the-
sis, Department of Information Engineering, CUA in Prague, The Czech Republic,
2005.
102 Tomáš Richta
Fig. 2. GeKon structure model
4. Mitrovic A., Djordjevic-Kajan S.: OO paradigm meets GIS: a new era in spa-
tial data management,invited paper, presented at YUGIS’96, Belgrade, Yugoslavia,
1996, http://www.cosc.canterbury.ac.nz/tanja.mitrovic/
5. Kofler M.: R-trees for Visualizing and Organizing large 3D GIS Databases, PhD.
Thesis, TU Graz, Austria, 1998.
6. Chance A., Newell R.G., Theriault D.G.: Smalworld GIS: An Object-Oriend GIS
- Issues and Solutions, Smallworld GIS white paper, 2000, http://www.logis.ro/
downloads/
7. Nebiker S.: Support for visualization and animation in scalable 3D GIS environ-
ment - motivation, concepts and implementation, scientific paper, International
Archives of the Photogrammetry, Remote Sensing and Spatial Information Sci-
ences, Vol. XXXIV-5/W10, 2003.
8. Kolbe T.H., Groeger G.: Towards unified 3D city models, article in: Proceeding
if the ISPRS Comm. IV Joint Workshop on ”Challenges in Geospatial Analysis,
Integration and Visualization II”’, Stuttgart, 2003.
9. Balovnev O., Breunig M., Cremers A.B., Shumilov S.: GeoToolKit: Opening the
access to object-oriented geo-data, scientific paper, Interoperating Geographic In-
formation Systems, Boston: Kluwer Academic Publishers, 1999.
10. Lurie G.R., Korp P.A., Christiansen J.H.: A Smalltalk-based Extension to Tra-
ditional Geographic Information Systems, students paper, http://www.dis.anl.
gov/geoviewer/, 1997