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Mapping
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A Topographic Database for Geo-information Production Process in the Survey Department of Sri Lanka
3.0 Way of Thinking
Digital technology was successfully introduced in the field of mapping in the late 1960's as means of speeding up map production and particularly the plotting and fair drawing phases. Changing technology in last two decades with the growing number of spatial information systems, the topographic database concept has been introduction in the several mapping and surveying organizations in the world in order to deliver more structural geo-information to the user community. Topographic database is a database which can store and update topographic information (spatial information) and relevant attributel information.
3.1The Process of the Database design
The design of a topographic database in a GIS environment, involves various phases such as
- Identification an analysis of user requirements
- Design of the general data model
- Design of the data collection model
- Selection of the physical model
- Design of the functional model.
3.11 User Requirement Analysis
Studies of user needs are essential for the preparation of the conceptual and functional models of the system design. By user requirement analysis it is possible to ensure that its database neither has insufficient information nor redundant information. In the course of such studies the following items should be considered.
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Assessment of the present information status
- Tasks performed by topographic information users and geographic regions of interest for their activities
- Types of the queries asked by the users and nature of operations where topographic information are used.
- User preference for information content, classification, form of presentation, accuracy and resolution
- Type of data commonly used, map scales their sources and method of data collection
- Need for information not provided by standard products (eg., conventional maps)
3.1.2.Data Collection Model
Defining of data collection specifications should carried out in this phase. These specification reflects system context and user requirements. It involves establishment of standards implementation such requirements. It involves establishment of standards implementation such as method of data collection, methods of quality control and design of "quality model", specification for hardware/software support.. etc.
3.1.4 Physical Model
This is the database management system which could processes for data structure and data retrieving. For this processes, specification should provide definition for the characteristics of the required tools such as equipment, system calibration model and program packages.
3.1.5 Functional Model
This is he tailored data model which support the user's view on the stored data sets and their application. In this phase operations/commands which will operate on the data stored in the physical model into the form required by the users.
4.0 Implementation of the Topographic Database Concept
As the first step, organization should conclusively identify the user needs as described in para 3.1.1 In conceptual modeling their requirement placed in the situation existing in reality to be identified. After finalizing the database contents, data collection model have to be designed as discussed in para 3.1.3. There are well established data collection methods in the department namely photogrammetric process and land surveying. The majority of data collected by using computer upgraded trained staff. Hence, the present data collection by using computer upgraded photogrammetric equipments with the well collection procedures can be further operationalised. In the field completion stage, data completion and verification, quality assessment, collection of information for further clarifications and labeling have to be done. Well trained surveyors are available in the organization to perform this reality (e.g : administrative boundaries) to be obtained from existing information and to be collected by manual digitizing.
There is a growing acceptance of the use of the topological model for the conceptual modeling of topographic features and the number of well known data structures have been built around this conceptual modeling of topograpahic features and the number of well known data structures have been built around this concept , the ARC/INFO system is an example. As a physical data model, UNIX ARC/INFO version is available in the department. After describing topographic features by a set of topological elements (nodes, arcs and polygons) to be stored in a non-redundant manner. The partial relationships of connectivity and adjacency are explicitly expressed and included in the ARC/INFO data structure (arc-node, left-right, polygon-arc topologies) as data item themselves. Therefore, data structuring can be done in the available UNIX ARC/INFO software.
Spatial indexing to data contents is a major issue. ARC/INFO MAP LIBRARY system can handle large volume of datasets as well as its tile structure provides spatial indexing to its contents. Main and auxiliary indexing system to be prepared for external users.
At the stage of presentation of these information to he users, the map, i.e. the end product of the standard production line to be prepared. In that case, although computers are available for map designing, however, the capable software have to be decided. Additionally, the staff involved in map designing have to be trained on digital mapping. Map reproduction and printing could follow the present manual production line. Special products/derived products can be obtained through the database and information presentation forms are graphics, display, reports and digital files. The issues related in disseminating of digital files are not discussed in this paper. Graphic output devices such as flatbed plotter and drum plotters (CALCOMP) vector and raster) are also available to prepare the hardcopy outputs from the digital database.
Data storing and archiving is a major concern in topographic database systems. Therefore, the required hardware and software and software capabilities for data conversion and transferring as well as staff knowledge and skills also needed.
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