Towards an Iranian Geospatial Data Transfer Standard Ahad Kheirabadi M.Sc. Student, Dept. of GIS Eng. a_kheirabadi0@yahoo.com  Ali A. Alesheikh Assistant Professor Dept. of Geodesy and Geomatics Eng. alesheikh@kntu.ac.ir Ali Aie M.Sc. Student, Dept. of GIS Eng. ali_aien@yahoo.com K.N. Toosi University of Technology Vali_asr St, Tehran, Iran, P.C. 19697 Tel: +98 21 878 6212 Fax: +98 21 878 6213 Abstract Geospatial data sharing is of vital importance for merging different agencies and organizations as it decreases duplications and reproductions of the data. One of the most important obstacles in this context is the absence of an efficient spatial data transfer standard. The purpose of this paper is to describe the steps involved in designing and developing a spatial transfer standard for Iran. Designing levels of geospatial transfer standard and its specifications are introduced. Existing geospatial transfer standards are scientifically analyzed. The analysis phase helps the project team to increase the speed of designing phase and decrease the associated risks. On the other hand a selected or developed geospatial transfer standard for Iran should comply with its existence data and data formats, so studying and assessment about them seem an important level in this case. The project is on going, and the paper discusses the current results of the research. 1. Introduction For the last several years, in our country, digital spatial databases have come to replace the conventional analogue data sources. During this time, it is understood that digital databases could support a wide number of purposes, systems and several applications especially in the GIS applications. To this end many countries and international organizations have developed spatial database transfer standard for their respective jurisdiction. To date more than 22 standards have been developed throughout the world. The main objective of this paper is to introduce standardized terminology and structure used for describing transfer standard, evaluating and comparing the major surface database transfer developed and approved in the world in one single source in common organized fashion and finally developing a transfer standard for Iran. Second part, the paper is dedicated for assessing and describing technical characteristics of standards for spatial data and databases. Next part of the paper contains the assessment of 10 major existing spatial transfer standards based on a crosstable which summarize the mentioned characteristics and evaluations. The last part of this paper indicates our recent efforts for developing a spatial transfer standard based on existing data and data formats which are used in the most important public, governmental and private organizations in Iran. 2. Technical characteristics for assessing spatial transfer standards As a definition, spatial transfer standard is a mechanism for archiving and transferring of spatial data and databases between dissimilar computer systems. The transfer process can be a complex and varied process. But there is a stable framework for spatial data transfer by defining different “levels,” from the real world to the physical encoding of the data (see Figure 1). The conceptual level describes a way to represent real-world entities, including their geometric and topological characteristics and relationships. The logical level presents a data model for identifying and encoding information for a transfer standard. A spatial transfer standard also defines the physical level with rules and specific formats for encoding data on a medium of choice (e.g., magnetic tape). Also each spatial transfer standard has own technical characteristics which describe their properties and specification.  Figure 1: Foundation for Spatial Transfer Standard. Technical characteristics are presented in the form of a questionnaire, designed to obtain information in a standardize format regarding the critical characteristics of a particular international standard. The questionnaire form should be included by administrative information, transfer context, transfer specification method, conceptual data model/schema, transfer process, transfer elements, update information, query information, quality information, feature / object information, attribute information, relationship information, and metadata information. So the technical characteristics have been organized into 13 categories. In order to facilitate user understanding of a standard, the categories of characteristics have been ordered beginning with rather general characteristics to increasingly more particular and detailed characteristics. The 13 categories of characteristics are as follow: Administrative information: This section provides information related to the administrative framework within which the standard was designed, developed and implemented. Information is provided about the official name and status of the standard, availability of official and supplementary documentation, software tools and training materials. Transfer context: This part explores the scope of the transfer context of the standard in terms of its major conceptual structure and whether it contains a conceptual data model and conceptual data schema, as well as things like a data quality model and spatial referencing. Then, a more detailed examination is made of the spatial types that are supported in terms of geometry/topology, dimensionality, semantics, time and whether one can specify user-defined data types. The basic design approach that is used and the sender/receiver relationship are also explored. Transfer specification method: Here the way in which the transfer standard is specified is examined in terms of whether is uses a formal or informal language, and how the standard is structured in terms of the number of components and how they are organized. The origins of the terminology used in the standard are also examined. Finally the table of contents from the standard is requested, which in some cases is several pages long. Conceptual data model/schema: The examination now turns to information relating to the scope of the data model(s)/schema that are encapsulated in the standard and whether it defines abstractions such as objects or features, semantics, structure or implementation. A diagram of the conceptual data model(s)/schema(s) is also requested as an aid to help the reader more completely understand the standard. Transfer process: Here the scope and organization of the transfer standard implementation is examined in terms of the transfer implementation used and open systems interface level that is addressed. The characteristic of self-description is examined in terms of its structure and content. Currently the more advanced standards are partly self-describing, while no standard is fully self-describing. That is for development in the future. A diagram is requested for the transfer metafile structure to facilitate reader understanding. Transfer elements: The nature of the spatial data elements that may be contained in a transfer metafile can shed much light on the kinds of spatial data that can be transferred by the standard. This begins with the spatial primitive by dimension, and then with aggregate spatial types, which are vector or tessellation-based. The kinds of data structures supported, graphic elements included, and details on spatial referencing in terms of coordinate systems, datum and projection are requested to give the user an idea of the breadth and complexity of the standard. Update information: a number of standards are designed to serve an update function in addition to transferring a full spatial database. Those are the ones that do supply information on the way in which the capability is specified and its functionality to add, delete, change or replace data. Some developers see this as an important function of their standard. Query information: The query capability is included in some standards to facilitate the extraction of data from a database. If that capability is contained in the standard, it is examined in terms of its conceptual specification and functionality that it is designed to accomplish. The question then turns to the performance and results that can be obtained from the query. Quality information: Quality information is provided by almost all standards in a rather substantial way. Items such as lineage, positional accuracy, logical consistency, attribute accuracy, completeness and currency are almost always provided. Additional elements are sometimes provided. The need for authoritative data quality information has been clearly organized in recent years, and these standards strive to provide it. Whether these elements can be provided by codes, and structures or unstructured text, and implemented at the individual primitive/object or aggregate levels is ascertained in the following subsections. Feature / object information: Real-word features or objects can be defined in the standard or by an external reference outside the standard, while many standards also permit user-defined features/objects. Attention is then focused on how the feature/objects definitions are defined, structured and encoded. Classes of feature/object definition are requested, and it is evident that most standard have lists of the features/objects classes that are defined and the number of items in each classes. Attribute information: Attributes can be handled in many ways, and its section examines how they are defined relative to the standard or external to it. The structure derivation and encoding of attributes and whether the definitions themselves can be included in a transfer are important to understanding the standard and its capability. Attributes are an essential part of any transfer, and most standards include a wealth of attributes that are associated with various feature/objects. Relationship information: relationship between various features/objects can occur in the real word in a very wide variety of ways. Many of these relationships are topological or semantic in nature. Information is requested as to whether the definitions are internal to the standard, external to it, or can be user-defined. As in the two above section, information is also provided relative to how these relationships are defined, structured and encoded. Metadata information: Metadata is one of the more elusive concepts for those learning about spatial and database transfer standards. Metadata is essentially data about other data. Data quality information is a kind of metadata that is important enough to have its own section above. However, much other information is usually contained in information modules that provide details about the transfer metafile that are in addition to the actual data being transferred. This section requests information on how this metadata is defined, structured and encoded. Each of mentioned categories is an essential part of any kind of spatial transfer standard. On the other hand, these characteristics do not resolve the very different uses of terminology between the various standards. This situation is compounded greatly because each national standard uses the official language(s) of the country in which it is being developed. One of the most complicated problems of terminology is the use of the words feature, entity and object. A similar problem occurs with instance and types of features, objects, attributes etc. The difference in such terminology between various standards is rather wide, and the best thing an examination of the characteristics of various standard can do is to record the terminology as used in a particular standard. 3. National and international transfer standard A major focus of this paper is the detailed assessment of the technical characteristics of spatial data transfer standards that are being developed throughout the world. These assessments have been organized into systematic parts with a question/ answer/ explanation style so that the structure of the characteristics can be understood in a comprehensive and compatible fashion. Since the parts have the same structure to them, individual characteristics of individual standards can be understood in a more general framework, while the same characteristic(s) between standards can be compared as well. The following are general comments on the 10 standards presented in the crosstable ( see table 1). Australia has developed AUS-SDTS, a modified version of the US Spatial Data Transfer Standard. It has been modified to use Australian horizontal and vertical datums, Australian data dictionaries and reference Australian external where appropriate. It is being established for use in both Australia and New Zealand. Canada has developed SAIF as the approved national standard for the entire country. As such SAIF contains a large number of designed capabilities that make it a very versatile, if somewhat complicated, standard. It is designed to harmonize with the SQL database developments, and the Open GIS (OGIG) efforts going on to promote GIS system interoperability. Japan has developed SPDFDM as a spatial data transfer format for use in digital mapping and photogrammetric surveying and mapping. South Africa has developed NES as a spatial data transfer mechanism to operate between a wide variety of spatial data systems with both raster and vector data. It uses a transfer mechanism based on a relational structure. United Kingdom has developed NTF to transfer vector and raster data with a flexible multilevel format between a wide variety of spatial data systems. United States has developed SDTS as an extremely flexible transfer mechanism between any kinds of spatial system by using a set of transfer profiles. To date, the Topological Vector Profile has been officially approved and the Raster Profile completed. An on line spatial feature register is available. CERCO has developed ETDB as a means of transferring topographical vector data from the European Territorial Data Base. The transfer is awaiting the development of a European Transfer Format (ETF). CENTC278/7 is developing the GDF standard under the DRIVE project for intelligent vehicle navigation with applications in the areas of road transport and traffic telematics (RTTT). DGIWG has developed DIGEST as a comprehensive transfer standard based on the family of formats approach to the task. As such, it contains several profiles, some of which are oriented toward specific production formats, and some which are somewhat more flexible. DIGEST supports more than 200 different horizontal datums and 15 different map projections. DIGEST has been put forward for adoption in several countries. IHO has developed S-57 for the transfer of vector hydrographic data than can be encoded at five different levels of topology. S-57 supports more than 100 horizontal datums and more than 20 sounding datums. Table 1 illustrates the technical characteristics of mentioned standards.     To design and develop a national spatial transfer standard for Iran, it is important to comply with technical characteristics that mentioned above. In order to satisfy this purpose, some questionnaire forms were provided to recognize and collect important information from Iranian major data producer such as National Cartographic Center (NCC), Iranian Remote Sensing Center (IRSC), National Geography Organization (NGO), Geological Survey of Iran (GSI), and Tehran GIS (TGIS) ( see in table 2). The collected information is features/objects types, existing and available formats, exporting formats, available software, quality information, horizontal and vertical datums, referencing systems, projections, attributes information, field and record types, database name or title, data model type (hierarchical, network, relational, object-oriented), saving format ( Access, Oracle, Dbase, FoxPro, Excel, text), Farsi available standard, available analysis metadata, existing spatial transfer standards information and its problems. In the next step these information will affect in the implementation case to design national spatial transfer standard. 
With wide speared acceptance of GIS in various organizations; and the needs to digital data sources, lead us to develop a mechanism for archiving and transferring of spatial databases between dissimilar computer systems. In the way of gaining such goal, standardized terminology and structure have been defined in the first step. Based on the collected standards, technical characteristics of each spatial transfer standard have been organized into 13 categories. Using a cross table and based on 13 categories and detailed aspects, most important national and international standard was evaluated. The evaluation shows that the existing standards do not possess all the characteristics but, contains a subset of them and absolutely it will be helpful to facilitate understanding of individual application. These sets of characteristics provide a uniform measure by which the various standards may be assessed. Future work has been started by preparing questionnaires and delivering them among various organizations. Collected data will be organized and analyzed for developing a national standard for solving transfer process in spatial data and databases in Iran. The authors of this paper wish to extend their gratitude to Iranian Remote Sensing Centre for their financial support to this project. 6. Reference
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