Page 1 of 2 Next  Prof. Arup Dasgupta Hon. Adviser, GIS Development and Distinguished Professor, BISAG, India arup.dasgupta@gisdevelopment.net Standards enable harmonious working across communities in the world. Technologies also need to evolve standards to meet new specifications. Geospatial data acquisition has moved from field surveys to aerial surveys to satellite observations. Observation systems have evolved from analogue instruments to digital sensors. Mapping technologies have also evolved from manual plotting to CAD, automated cartography and digital photogrammetry. Spatial analysis is another field where computers and DBMS have brought in a revolution through the development of geographical information systems. Data standards have always been an integral part of these advances. In the past the process of standardisation had been implemented in parts. Further these standards were dictated by regional, technical and application considerations. Consider the case of the reference ellipsoid. It was well known that the earth's surface was an irregular spheroid and it was necessary to model it in mathematical terms to be able to map it. Initially each country developed its own ellipsoids based on celestial measurements. Thus we had separate ellipsoids for India, America, Europe and so forth. The development of satellite geodesy resulted in the evolution of the WGS global reference ellipsoid which has now become the global standard. All other ellipsoids are now related to the WGS ellipsoid through mathematical models. Similarly, the map projections required to transfer the ellipsoid to a planar surface also evolved as per the needs. Navigators found the Mercator projection most useful as it gave true bearings. However, when area and linear measures were of importance the preferred projections were those that preserved these characteristics. It is therefore not surprising that there are more than 400 projection systems! Mapping itself involved laborious field observations and then transferring these to a two dimensional representation based on the reference ellipsoid and projection. The advent of aerial photography and satellite remote sensing brought in a new dimension to data acquisition and therefore new standards. Cartography, the technique of creating two dimensional graphic representations from this data, also developed its own standards as it progressed from manual methods to analogue and then digital techniques. Map analysis received a boost as digital methods enabled the creation of data bases of different maps and their conjunctive analysis. Here too the technology progressed from file based systems for fast access on slow computers to geo-relational databases which linked graphic files to standard relational databases. Standards were set by the technology used and were limited to an organisation. Today, fully relational spatial databases and fast desktop computers have made spatial data commonly available. Therefore it has catalysed the development of standards which cut across institutional, community and regional barriers. Standardisation efforts begin at national level. Thus we have the Canadian Geospatial Data Infrastructure, the National Spatial Data Infrastructures of the USA and India, the European Committee for Standardisation, CEN and many others. The International Standards Organisation, ISO set up a Technical Committee 211 to address the standardisation in Geomatics. The ISO standards are based on the experience and best practices of different countries and are very comprehensive. ISO standards are guidelines which need to be followed in developing national standards to enable interoperability and future-proofing of systems as new technologies emerge. Another international body, the Open Geospatial Consortium consisting of nations, industries and academia works in tandem with the ISO and develops tools, methods and processes to help institutions implement the ISO guidelines. A very useful document prepared by the Federal Geographic Data Committee, FGDC, of the United States of America is the Geospatial Interoperability Reference Model which references ISO standards and OGC specifications for interoperability of distributed geospatial data over the Internet. As can be seen from the above description, the process of standardisation must cover all aspects from data acquisition to pre-processing to database creation, usage and information delivery. This is summarised in figure 1. Standards need to be developed for each module such that the data flow becomes smooth and seamless. The process of standardisation must begin with the selection of the reference datum and the preferred map projections. Large areas will require the maps to be tiled and referenced to a geographical framework but the provision must exist to be able to access the data seamlessly across tile boundaries. The combination of datum, projection and map tiles form the national spatial framework. The following specific standards need to be addressed:
 Fig.1 The data process flow
Page 1 of 2
Next |