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Open Geospatial Datastore Interface (OGDI): A geospatial data infrastructure solution
2. Solving the Geospatial Data Barrier Problem
Billions of dollars have been invested worldwide in the production of geospatial datasets. These datasets have been developed for a large variety of application domains, such as municipal planning, forestry, mining, environmental, and military command-and-control applications. Each of these applications has specific requirements (e.g., raster or vector representation, level of detail, set of coverages, projection, datum), so the datasets have been produced in a variety of formats, in many cases targeted at specific GIS packages.
In order to take advantage of existing data and to minimize production costs and the duplication of effort, geospatial data must be shared. Because data conversion and integration costs are high, two solutions have been developed through the years to solve the geospatial data barrier problem: data translation and data standardization.
- Geospatial data translation
In most cases, GIS developers have developed their own proprietary geospatial data format, specifically designed to speed up the display and query of data in their particular systems. Their solution to the geospatial data barrier problem is the use of ethnocentric translators that convert foreign geospatial data formats into their own format. Although this provides a certain level of interoperability, there are several drawbacks:
- Lost of significant information because of different degrees of completeness.
- Duplication of effort by vendors who must write translators for the commonly used geospatial data formats.
- Duplication of effort by data suppliers who have to develop tailored versions of their geospatial data products for several software packages.
- Adoption of incomplete de facto industry standards because of difficulty and cost of data integration.
- Geospatial data standardization
Over the past several years, users have been encouraged to adhere to a set of international geospatial standards and thus to minimize the number of geospatial data formats in the marketplace, in order to reduce duplication of work, optimize resource expenditure and facilitate information exchange.
A number of digital geospatial data exchange standards have been developed, and although their use does not completely eliminate the need for translators, it does provide better interoperability by specifying the information to be exchanged. Among the most interesting of them, in terms of completeness, flexibility and life expectancy, are:
- the DIgital Geographic information Exchange STandard (DIGEST);
- the Spatial Archive Interchange Format (SAIF); and
- the Spatial Data Transfer Standard (SDTS).
Standardization is a positive step toward solving the geospatial data barrier, but by itself it isn't enough, since it is highly unlikely that the industry will move to a single standard. It is more probable that at least a half-dozen principal standards will coexist. Moreover, billions of dollars of legacy datasets must continue to be supported.
- Open GIS frameworks
Over the last three years, significant initiatives have been taken to address the geospatial interoperability issue at a more global level than just the geospatial standard. In addition to national initiatives on spatial data infrastructures, three important bodies are conducting work on GIS frameworks, in order to improve geospatial interoperability:
ISO/TC 211. ISO/TC 211, is an international effort to establish industrial and world standards in geomatics. TC 211 provides a politically neutral forum for all proponents to align their respective standards.
OGIS. The Open GIS Consortium is an open forum for the GIS community to contribute to the interoperability in geodata and operations [Buehler et al. 1996].
DGIWG. The Digital Geographic Information Working Group (DGIWG) promotes the use of DIGEST by providing a set of freeware tools, interoperability over geospatial data, direct and transparent access (platform and projection independent) to DIGEST-compliant data, and a worldwide data access through communications networks (Internet/Intranet, local and wide area networks).
The Department of National Defense, in partnership with Global Geomatics Inc has been developing the DIGEST Geo Components to promote the use of DIGEST. A key component, the Open Geospatial Datastore Interface (OGDI), provides a good solution to the geospatial data barrier problem.
3. Open Geospatial Datastore Interface (OGDI)
As has been described in the previous sections, the geospatial data barrier problem exists because various geospatial data products, in different formats and cartographic projections, coexist and need to be integrated. In a way, the situation is analogous to the multiplicity of languages that coexist. Multilingual people can share information with each other without having to translate into their mother tongue. For example, if English-speaking people were to learn to read Chinese and vice versa, nobody would have to learn to write Chinese; the Chinese would know how to read English.
Applying this "learn foreign languages instead of being ethnocentric" theory to geospatial data has led to the Open Geospatial Datastore Interface (OGDI). Using OGDI, different geospatial data formats can be read without any translation or conversion.
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