Developing with Standard Geospatial Interfaces
Discovery and access
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A VH exposes a set of standard geospatial interfaces that an application can access. The specific type of exposed interfaces is defined by the VH manager. A user can check the exposed interfaces through the VH technical information page accessible at:
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http://vh-eu.energic-od.eu/gi-cat/
The VH technical information page has a section named Published interfaces which lists the available catalog interfaces for discovery providing the identifier of the adopted specification and the endpoint.
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Example of information on the standard interfaces exposed by the VH with their endpoints
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A sample entry is:
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CSW/ISO 2.0.2 interface
Endpoint: http://gi-cat.virtualhub.essi-lab.eu/gi-cat/services/cswiso?
Capabilities document
It says that the VH exposes a CSW/ISO 2.0.2 interface at the endpoint http://gi-cat.virtualhub.essi-lab.eu/gi-cat/services/cswiso?. CSW/ISO 2.0.2 means that the interface is compliant with the version 2.0.2 of the Catalogue Service for Web defined by the Open Geospatial Consortium, and the metadata model is ISO (ISO 19115). The documentation is available through the web sites of the standard organizations. In this case, for example, the OGC CSW 2.0.2 specification is accessible at http://www.opengeospatial.org/standards/cat and the ISO 19115 specification is accessible at http://www.iso.org/iso/catalogue_detail.htm?csnumber=53798.
All the discovery interfaces provide a list of datasets published through the VH. If the dataset is accessible, the description of each entry provides one or more access services to download the dataset. The list includes the original access services to download the dataset from the data provider, and one or more specific entries to download the dataset through the VH. Using one of these latter entries it is possible to exploit the VH access capabilities such as the dataset transformation (subsetting, interpolation, resampling and format change) even if the original server is not able to provide such capabilities. Figure 6 shows an example of dataset description as presented by the VH portal. The Links section reports three access links. The first one is the original OGC WMS service exposed by the data provider; the second one is an access service provided by the VH through a proprietary advanced interface (named GI-axe); the third one is a standard compliant OGC WMS service exposed by the VH.
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An example of dataset description as presented by the VH Data Portal
A user who is expert in geospatial technologies can develop an application compliant with the specifications supported by the VH. Figure 7 shows an example of an application interacting through two standard interfaces with the VH and with one of the original data sources.
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An example of application interacting with the VH through standard interfaces
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