Implementation of Object Approach In Modelling Of Croatian Topographic Information System - Crotis Zvonko Biljecki Geofoto LLC Buzinski prilaz 28 Zagreb, Croatia zvonko@geofoto.hr Aida Osmanagic Geofoto LLC Buzinski prilaz 28 Zagreb, Croatia aida@geofoto.hr Daniel Vencler Geofoto LLC Buzinski prilaz 28 Zagreb, Croatia daniel@geofoto.hr Abstract: The Croatian Topographic Information System - CROTIS encompasses the standardization of topographic spatial data. The final goal is setting up a flexible and simple but high-quality geoinformation system based on modern technologies of modeling real-world, with an emphasize on functionally significant objects in management of human environment. The backbone of the system is object oriented spatial database is meant to be the basic topographic information system of the Republic of Croatia containing the information that majority of users would need as the basis for creation of specialized information systems. Currently, CROTIS is modernized and synchronized with the latest ISO and OpenGIS standards in order to develop procedures for topographic data distribution by using GML (Geography Markup Language). Project CROTIS-GML encompasses new data model which is made according to ISO 19109 standard and described in UML. Application schema in UML defines logical structures of data and operation that can be preformed on or with the data. Format for data distribution is GML. GML is generated automatically from the data model. 1. Introduction The main principles and guidelines of Croatian Topographic Information System (CROTIS) have been set up in 1996 as one of the most important component of STOKIS (Official Topographic and Cartographic Information System of Republic of Croatia) conceptual project defined in 1995. The CROTIS project encompasses the standardization of topographic spatial data giving basic and detailed solutions of topographic information system in the field of data models, data capturing, processing, accuracy, topological relations and data exchange. In December 2000, version 1.0 of CROTIS has been published containing four major parts; data model with data capture criteria, topological relations, data exchange rules and object catalogue. The version 1.1 of CROTIS in which were added some new classes has been published in November 2001. On the 1st February 2002 CROTIS became the Standard for the capturing, processing and storage of spatial information. The data is loaded into the spatial database proving CROTIS functionality and setting up foundations for more detailed product specifications developed and released in May 2003. The fundamental guideline of this approach is to point out, give more weight to presenting and gathering the data having great importance for the exploitation and management of space. Functionally less important objects (concrete path between two buildings or family house staircases) do not present object classes of official topographic geoinformation system because their function does not make them essential objects for the space management. Today, together with product specifications, CROTIS represents the national framework for capturing, processing and controlling of topographic data in 1 m accuracy and it is modernized and synchronized with the latest ISO and OpenGIS standards in order to develop procedures for topographic data distribution by using GML (Geography Markup Language). 2. Data model overwiew The heart of any GIS is the data model, which is a set of constructs for representing objects and processes in the digital environment of the computer. The conceptual modelling is based on using abstraction, i.e. on the basis of methodology established by concentration applied in recognising the similarities among objects of the real world and temporary neglecting of differences among them. The abstraction is used to decompose the model of the real world, objects and connections among them, in the hierarchy of abstractions, i.e. into the combination of aggregations and generalisations.  Figure 1. The role of a data model in GIS [1] When representing the real-world, it is helpful to think in terms of four different levels of abstractions. First, the reality is made up real-world phenomena (buildings, streets, etc.) and includes all aspects that may or may not be perceived by individuals, or deemed relevant to a particular application. Second, conceptual model is a human-oriented, often partially structured, model of the selected objects and processes that are thought relevant to a particular problem domain. Third, the logical model is an implementation-oriented representation of reality that is often expressed in the form of diagrams and lists. Physical model portrays the actual implementation in a GIS, and comprises tables stored as files or databases [1]. 3. Standards in Geoinformatics Standardization in Geographic Information System is necessary for the purpose of establishment of a uniform system, production, maintenance, presentation and exchange spatial information in digital form between different producers, users, systems and locations. Technical commitee 211 of International Standard Organization (ISO) has the main role of standardization in the field of geoinformation. The following ISO standards were used for the production of CROTIS project.
GML characteristic are:
Establishment of CROTIS as the national standard, defined the way for setting up the geoinformation system in the domain of topography and geoinformation. The goal of new project «CROTIS-GML» is adaptation of CROTIS model with latest standards, consider the tendencies of changes other national topographic standards, which are conditioned with new standards and rules. The study of old data model was refered to the implementation form. The content of data model, within the meaning of adding new classes or attributes was not changed. Implementation part related on new approach in describing of data model with conceptual schema language, new data catalogue, new data exchange language. The first part was UML data model which describes classes, attributes and their values. The Unified Modeling Language (UML) is the object modeling and specification language used in developing models, softwares, etc. UML includes a standardized graphical notation that may be used to create an abstract model of a system: the UML model. It is important to distinguish between the UML model and the set of diagrams of a system. A diagram is a partial graphical representation of a system's model. UML has its strengths at higher, more architectural levels and has been used for modeling of wideband area of business process such as use for business process modeling, systems engineering modeling, and representing organizational structure. New CROTIS model was made according the rules of conceptual schema language and application schema language in UML. GML application schema and data catalogue were atomaticaly generated from UML. UML doesn't contain enough information for data generation, so as to ensure above mentioned products we added some aditonal attributes. That means, all data which are not contained in UML such as code for compabillity, definition, etc. were added later in UML application in order to get generated products. UML is approving of object-oriented modeling and possibilities of extensive applyings . The figure 2 shows data flow and method of project execution  Figure 2. Schema of adaptation of CROTIS data model 5. Processes of adaption CROTIS data model 5.1. Transformation of model Analysis of previous data model CROTIS version 1.1 resulted with divergance with model specified in ISO. The differences between old version and new version of data model are presented on the figures 3. The data modeling was accomplished through appllication schema prescribed in ISO 19109 standard. Conceptual schema language contains objects which are described in ISO 19103 standard. Geometry schema is accepted from ISO 19107 standard. The previous version of data model was conceived through following tables:
In that case two separate tables show the objects and their properties. Such tabular data model doesn't allow any kind of automatic generation. The goal is to get a model which enables more then common tables.  Figure 3. Transformation of old data model to new one The purpose of application schema and new modeling is:
Documentation generator The Catalogue of Object Classes presents all objects that make an integral part of a certain geoinformation system according to the adequate classification. Obligatory attributes and criteria for their gathering, as well as accuracy and geometric presentation are the essential elements that a creator of computerised reality has to take into consideration permanently. The data catalogue is generated automaticaly from data model. The standard ISO 19110 presents the template for the organization of feature catalogue information according to rules described by standard. The figure 4 shows standard ISO 19110. Some elements are mandatory (M), conditional (C) or optional (O) and can be included in the feature catalogue.  Figure 4. ISO 19110 [5], data catalogue GML schema generator The project CROTIS determines the manner of data exchange within the frame of topographic information system. The contents of standards include defining the schemes for data exchange, execution mechanisms and data encoding rules. The standards define the following items:
In the meantime OpenGIS consortium developed specification for GML and currently ISO is accepting and developing GML as ISO standard. The Geography Markup Language (GML) is an XML encoding in compliance with ISO 19118 for the transport and storage of geographic information modelled according to the conceptual modelling framework used in the ISO 19100 series and including both the spatial and non-spatial properties of geographic features [6]. The specification defines the XML Schema syntax, mechanisms, and conventions. The data from topographic database is presented through web portal which prototype is made, for the purpose of different users such as: Companies producing topographic maps, Land use planning departments of the regional and local communities, Private companies producing “derived” maps or databases, Hydrography, road and railroad authorities, Large state owned and private companies, exploiting natural resources, Ecology authorities and organisations, Tourist and recreational organisation and local authorities, Ministries, Croatian Air Traffic Control, Croatian Waters, Municipalities, Utility companies, etc. The mentioned users can review the data and download the data sets in GML. For the review of data they need only web browser. All of them can have some extra permissions for downloading the data. Downloaded data in GML can be open with the tools which support GML. The figure 5 shows exapmle of topographic database and web application of topographic data.  Figure 5. Database and Web GeoApplication – topograchic data 6. Conclusion CROTIS represents the national framework for capturing, processing and controlling of topographic data. Now, CROTIS is modernized with latest ISO and OpenGIS standards. In the feature it will be backbone for the area management and planning. New data model, generated data catologue, generated GML application schema are products of project CROTIS – GML. New data model encompasses the topographic data described in UML. UML allows export to more specified applications such as is Documentation and GML application schema. GML is using for data exchange where users can download the data and by itself create different kind of Geoinformation Systems. 7. References
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